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!^vjijz INVERTEBRnlL 7

vZOOLOGY/

T H p:

VOYAGE OF H.M.S. CHALLENGER.

ZOOLOGY.

REPORT on the Isopoda collected l)y H.M.S. Challenger during the Years
1873-76/ By Frank Evers Beddard, M.A. (Oxon.), F.R.S.E.,
F.R.M.S., F.Z.S., M.B.O.U., Prosector to the Zoological Society of
London.

PART I.-THE GENUS SEROLIS.

PEEFACE.

Among the Isof)oaa collected duriug the Challenger Expeditiou the genus Serolis
occupies a very prominent position both as regards number of specimens and of new
species ; for this reason I have thought it advisable to separate Serolis from the rest of
the group, which will be treated of in the second part of my Report.

As many as sixteen diflerent species were collected during the voyage, of which nine
are new. One of these new species was named Serolis hromleyana, and briefly described
by the late Dr. von Willemoes Suhm in his Preliminary Report on Crustacea observed
during the voyage of H.M.S. Challenger ;' the remaining eight have already been briefly
noticed by myself^

Into the systematic part of this Report I have also introduced some account of the
remaining species of the genus that were nut obtained by the Challenger in order to make
the Report more complete.

The portion which deals with the internal anatomy of Sovlis is unfortunately very
incomplete ; the specimens were not very favourably preserved for anatomical investiga-
tion, and I did not feel justified in using a great amount of material.

' Proc. Umj. Soc. LonJ., vol. xxiv. p. 585, 187(i. - Proc. Zool. Sue. Loud., pt. iii. p. 330, 18S4.

; (zOOL. CHALL. EXP. PART. XXXIII. 1884.) Kk 1

nl

2 THE VOYAGE OF H.M.S. CHALLENGER.

A discussion of the systematic position of the genus Scrolis within the order Isopoda
will be best postponed until after a more detailed study of the remaining part of the
collection.

With regard to the alleged affinity of Sewlis (and of the Isopoda generally) for the
extinct Trilobites, insisted upon by Milne-Edwards/ I have nothing to add to what has
already been said ; the examination of the Challenger collection of SeivUs has brought to
light no facts which tend to show any close resemblances between the two groups.

I have to thank Mr. E. J. Miers of the British Museum for kindly facilitating my study
of the specimens of Serolis preserved in the national collection.

HISTORICAL NOTICE.

The first recorded notice of Serolis is contained in Fabricius's Systema Ento-
mologise, which was published in 1775. Under the name of Oniscus paradoxus is a
short description of a species subsequently named Serolis fahricii by Leach, and wlii(;h
was obtained at the Straits of Magellan during Captain Cook's second voyage.

A few yeai's later (1767) Fabricius briefly defined this species in his Mantissa
Insectorum ; in both these works Oniscus is placed in the class Synistata, which forms
the third class of the four into which Fabricius divided what are known now as Arthro-
poda, and which included, besides the Isopoda, the majority of the Insecta now classed
within the orders Hymenoptera, Diptera, and Heteroptera.

In his Species Insectorum, published in 1781, Fabricius gave another description
of this species, still under the name of Oniscus 2}ci'>'ctdoxus ; here Fabricius hints at the
Trilobite affinities of the genus " An protypon Entomolithi paradoxi ? In multis
certe convenit."

In 1798 appeared Fabricius's Entomologia Systematica, which is a considerable advance
upon his earlier works. His eighth class, Polygonata, includes all the Crustaceans belong-
ing to Latreille's order Isopoda as well as the genus Monoculus r the name Oniscus
paradoxus is altered to Cpnothoa paixtdoxa, and a fuller definition of the genus is given.

Fabricius's Ci/mothoa paradoxa was first recognised as the type of a new genus by the
English naturalist Dr. W. E. Leach; in the twelfth volume of the Dictionnaire des
Sciences Naturelles, published in the year 1818, is an article by Leach on the Cymothoadte,
where Cymoihoa paradoxa is redescribed under the name of Serolis fahricii.

In 1825 Desmarest in his Considerations generales sur les Crustaces recapitulated
Leach's description of Serolis fahricii. Both Desmarest and Leach denied the supposed
affinities of Serolis with the Trilobites.

In 1833 James Eights described in the Transactions of the Albany Institute, vol. ii.

' Arch. d. Mas., t. ii. p. 5 ; Aim. d. Sci. Nat., sir. 6, t. xii. art. No. 3.
- MonocHhis includes all the members of the order Eiitomostraca.

REPORT ON THE ISOPODA. 3

p. 53, pis. i. and ii., another species of Serolis under the name of Brongniartia triJo-
hitoides, which name was subsec[iiently altered by Audouin and Milne-Edwards into
Serolis trilohltoides, since there was evidently no generic difference from Serolis para-
doxa ; this paper contains merely a description of the new form, accompanied by figures
ill which the whole animal as well as the mouth appendages and the two first abdominal
limbs are displayed ; a figure of a Trilobite, Paradoxus boltoni, is given for the purpose of
comparison, but there is no account in the text of any supposed resemblances between
the two forms, except the similarity of the eyes. It seems not unlikely that this species
is identical with Studer's Serolis cornvta, or at most a local variety. This species was .
obtained on the coast of Patagonia from the stomach of a fish belonging to the genus
Phycis, and also from the South Shetlands.

The next contribution is a paper by Audouin and Milne-Edwards, which was pub-
lished in the Archives du Museum for 1S41. This important memoir on the genus
Serolis contains, after an historical introduction in which all the previous notices regard-
ing the genus are reviewed, a general account of its external characters, and a description
of four species — Serolis paradoxa, Serolis trilobitoides, Serolis orhignyi, and Serolis
gaudicJiaudii, the two last being here described for the first time ; the memoir is illus-
trated by figures of these species and of all the essential parts in their anatomy ; with
regard to the afiinities of the genus, it is considered as intermediate between the other
Isopoda and the Trilobites. Several of these figures are repeated in the magnificent
illustrated edition of Cuvier's Eegne Animale, edited by his disciples Audouin, Milne-
Edwards, Latreille, &c., though the text of this work appears only to contain a descrip-
tion of Serolis paradoxa.

The Histoire Naturelle des Crustaces of Milne-Edwards, published in 1840, contains
a description of the genus Serolis and of the four species Serolis fahrieii { = Serolis jxira-
doxa), Serolis bronr/uiartiana { = Scrolls trilobitoides), Serolis orhigniana, and Serolis
gaudichaudii ; in this work Serolis is included in the family Cymothoadaj, which is
divided into three tribes — (l) Cymothoadiens ravisseurs, Serolis; (2) Cymothoadiens
errans, ^ga, Conilera, &c. ; (3) Cymothoadiens parasites, Cymothoa, Nerocila, &c.

In 1852 Dana described a new species of Serolis {Serolis -plftnits) in the Crustacea of
the United States Exploring Expedition.

Six years later (1858) another species was described by Liitken, to which he gave the
name of Serolis sehythei.

The next and a most important contribution to our knowledge of Serolis is Grube's
Monograph of the genus, published in 1875. Besides the description of a new species
[Serolis tubercidata), a general resume of the extei'nal characters of the genus, and some
notes on certain species {Serolis paradoxa and Serolis sehythei) that had been previously
described, are to be found in this paper, together with a complete list of the then known
species, eight in uumljcr. Grube regards Serolis as being most nearly allied to SphcBroma.

4 THE VOYACxE OF H.M.S. CHALLENGER.

During the "Transit of Venus" Expedition to Kcrguelen in 1875, two species of
Serolis were obtained, which were figured and described by Miers, one of these— *Serofc
septemcannata — being new.

About the same time the German ship " Gazelle " collected a number of species of
Serolis both at Kerguelen and on the shores of South America, which were described by
Studer' in 1879. This paper contains, besides the description of a new species (Serolis
cornuta), a few notes upon the habits of these animals and upon some points in their
anatomy.

A few notes upon certain of the species of Se)-olis that are described in the present
Keport are to be found in v. Willemoes Suhm's Preliminary Report upon the Crustacea
collected during the voyage of the Challenger.'''

Finally, a recently published part of Bronn's Thierreichs (Bd. v. Abth. 2, Heft i.-x.)
contains a general account of the Isopoda by Prof A. Gerstaecker, where some description •
of the genus Serolis, especially of the geographical distribution, is given ; there are also
in this work a number of figures copied from the Memoirs of Grube and Studer; and a
compai'ative view of the various schemes of classification of the order Isopoda ; for this
reason I have not in the present Report entered into any account of the systematic
positions which have l)een assigned to the genus Serolis Ijy previous writers.

1 Archivf. Natiiryesch., .lahrg. xlv. Bd. i. p. 11)4.
- Proc. Roy. Soc. Lond., vol. xxiv. p. 585, &c., 1876.

BIBLIOGRAPHY.

The followius; list contains a reference to most of tke treatises and memoirs which
contain any description or figm-es of Serolis. I have not attempted to include all the
works in which the name of the genus is merely mentioned ; I think, however, that no
paper of importance has been omitted.

1775. Fabricius, Systema Entomologia?, p. 296. ' Fleiifhurgi et Lipsiw.

1787. Fabricius, Mantissa Inseotorum, t. i. p. 240. Hafnue.

1789. Olivier, Article " Aselle" in EnoyclopeJie MetlioJique, t. i. p. 252. Paris and Liege.

1793. Fabricius, Entomologia Systematiua, t. ii. p. 503. Ha/nice.
1818. Leach, W. E., Dictionnaire des Sciences Naturelles, t. xii. p. 339.

1825. Desjiarest, Considerations generales .sur la Cla.sse des Crustaces, p. 292. Parif.

1829. Latreille, Eegne Animale de Cuvier, t. iv. p. 132. Parts.

GuERiN, Article " Serole," Dictionnaire classique d'histoire naturelle, t. xv. p. 372.
1833. Eights, James, Description of a New Crustaceous Animal found on tlie Shores of the South Shetland

Islands, with Eemarks on their Natural History. Trann. Alliamj hut., p. 53.

1836. CuviER, G., Le Eegne Animale, S""" lid., t. ii. p. 213. Bnuxelleg.

BucKLAND, Geology and Mineralogy, vol. i. p. 392. London.

1838. La-Marck, Hist. Nat. des Animaux sans Vertebres, 2"" ed., t. v. p. 291. Paris.

1840. ^Iilne-Edwards, H., Histoire Naturelle des Crustaces, t. iii. p. 228. Pans.
CnviER, G., Le Eegne Animale, Les Crustaces avec un altas par. JL Milne-Edwards, p. 193,

pi. Ixiv. figs. 2, 3. (No date) Paris.

1841. AuDouiN ET Milne-Edwards, Description des Crustaces nouveaux ou peu connus, &c. Arch. d. Mas.

d'Hist. Nat., t. ii. p. 5, pis. i., ii.
1843. White, A., Description of New Species of Insects and other Annidosa. Ann. and Mac;. Nat. Hist.,

vol. xii. p. 346.
1852. Dana, J. D., United States Exploring Expedition — Crustacea, pt. ii. p, 794, pi. liii. tig. 1.
1858. Lutken, Chr., Beskrivelse af en ny Scrolls — Art. Vidensk. Meddrl. / d. md. Foren. i Kj\'ib/'nhavi/,

1858, p. 98, pi. i.
1866. Schiodte, J. C, Krebsdyrenes Sugemund. Kn^yer, Nat. Hist. Tidsslr., Eidvk 3, Bd. iv. p. 109, pi. x.
18G8. Schiodte, J. C, Un the Structure of the Mouth in Sucking Crustacea. Ann. and Mag. Nat. Hist.,

ser. 4, vol. i. p. 1, pi. i.
1868. Cunningham, E. 0., Letter from, to :\Ir. Spence Bate. Ann. and Mag. Nat. Hist., ,ser. 4, vol. i. p. 442.
1871. Grube, E., Bemerkungen uelier Lumbrico-nereis gigantea Qi.1 und eine neue CEnone (Oinone vitiensis)

und SeroUs (Serolis acutangula). Jalin'sti. schles. Gesellsch., pro xlix., 1871, p. 56. Brcslan.

1871. Cunningham, E. O., Eeptiles, Fishes, Mollusc;i, and Crustacea obtained during the voyage of H.M.S.

"Nassau" (1865-69). Trans. Linn. Soc. Land., vol. xxvii. p. 498, pi. lix. fig. 3.
1874. AVillemoes Suhm, E. von. Von der Challenger Expedition. Briefe an ('. Th. v. Siebold ; a series of

letters in Zeitsc/ir. f. iciss. Zoo/., Bd. xxiv., xxv., xxvi., xxix.

6 THE VOYAGE OF H.M.S. CHALLENGEE.

1875. MiERS, E. J., Descriptions of New Species of Crustacea collected at Kerguelen Island by the Eev. A. Eaton.

An7i. and Mag. Nat. Hist., ser. 4, vol. xvi. p. 73.
KiDDEU, J. H., Contributions to the Nat. Hist, of Kerguelen Island — Crustacea, by S. I. Smith. Bull.

U. S. Nat. Miis., 1875, p. 63.
Grube, E. a., Beitrag zur Kenntniss der Gattung Serolis. Archivf. Naturgescli., Jahrg. Ixi. Bd. i. p. 208,
pis. v., vi.

1876. LocKiNGTON, W. N., Remarks on the Crustacea of the Pacific, with Descriptions of some New Species,

p. 208, pis. v., vi. Proc. Calif. AcaJ. Nat. Sci., vol. vii. p. 36.
MiERS, E. J., Catalogue of New Zealand Crustacea, p. 117, pL iii. fig. 7. Londun, 1878.

Studbr, Th., Ueber neue Seethiere aus dem Antarktischen meere. Mittli. Naturf. Gesdlsch. Bern,

1876, p. 75.
WiLLEMOES SuHM, R. VON, On Observations made during the earlier part of the Voyage of H.M.S.

Challenger. Proc. Roy. Soc, vol. xxiv. p. 569.
WiLLEMOES SuHM, R. VON, Report on Crustacea observed during the cruise of H.M.S, Challenger.

Proc. Bo;/. Soc, vol. xxiv. p. 585.
ScHMELZ, Serolis tuberculata, Gr., und Serolis orbignyana. And. et Edw. Journ. Mus. Godi'ff., part xii.

p. 161.

1877. LuoAS. Ball. Ent. Frurir., 1877, p. 146.

GiGLioLi, Enrico, Viaggio intorno al globo dclla Magenta, p. 956. Mihni.

1879. Sthder, Th., Die Fauna von Kerguelen's Land. Archin f. NaturgcscTi., Jahrg. xlv. Bd. i. p. 104.

MiERS, E. J., Crustacea, in An Account of the Petrologioal, Botanical, and Zoological Collections made in

Kerguelen's Land and Roddguez during the Transit of Venus Expedition. Phil. Trahn.,

vol. clxviii., extra vol., p. 200, pi. xi.
Studer, Th., Beitrage zur Kenntniss nioderer Thiere von Kerguelen's Land. Arcliiv f. Naturgescli.,

Jahrg. xlv. Bd. i. p. 19, pi. iii.
Milne-Edwards, A, Compte rendu des recherches sur la faune de I'lle de Kerguelen, faites par les

niembres de I'expedition astronomique. Ami. d. Sci. Nat., ser. 6, t. viii.

1881. MiERS, E. J., Crustacea collected during Survey of H.M.S. "Alert." Prnc. Zool. Soc. Land., 1881, p. 61.

1882. LiJTKEN, Chr., Dyreriget, p. 468, with fig. Kjohenham.

1883. Bronn's " Thierreich's," Bd. v. Lief 1-10, 1881-83, pi. v. figs. 4-9. Le.ipdc and Heiddherg.
Studer, Th., Isopoden gesammelt wiihrend der Reise S. M.S. " Gazelle " um die Erde 1874-76. Ahhandl.

d. k. Al-ad. d. Wisi. Berlin, 1883, pp. 1-28 with 2 pis.

1884. Beddard, F. E., Preliminary Notice of Isopoda collected during the Voyage of H.M.S. Challenger.

Part I. The Genus Serolis. Proc. Zool. Soc. Lond.. 1884, pt. iii. p. 330.

DESCRIPTION OF THE GENUS.

Serolis, Leacli.

Oniscus, Fabricius, Mantissa Insectorum, p. 240, 1787. In Part.
Asellus, Olivier, Encycl. ^I6th., t. L p. 2.52. In Part.

Gymothoa, Fabricius, Entomol. Syst., ii. p. 503, 1793. In Part.
Serolis, Leacli, Diet. d. Sci. Nat., t. xvii. p. 340, 182.5.
Bronijniartia, EigMs, Trans. Alb. Inst., ii. p. 53, 1833.

Definition. — Body much depressed, round or oval iu form, usually furnished with
long sickle-shaped epimera. Cephalic shield broad, terminating anteriorly in a short
median rostrum, uniting with first two segments of thorax to form a cephalothorax.
Terminal segment of thorax rudimentary, its tergum unrepresented ; sternum partially
fused with that of preceding segment ; epimera absent. Abdomen consisting of three free
segments and a caudal shield ; first segment devoid of epimera, and completely enclosed by
the preceding and succeeding segments ; second and third segments with longer or shorter
epimera. Caudal shield usually pentagonal, with one or more longitudinal carin^e, rarely
smooth. First pair of antennse subequal in length to .second pair, the former with four
basal joints and a multiarticulate tiagellum, the hitter with five basal joints and a multi-
articulate flagellum. Mandibles stout and strong, with a long three-jointed palp. Maxillne
small and delicate. Maxillipedes large and operculiform, entirely covering maxilte.
Ambulatory appendages seven pairs ; anterior pair (in male second pair also) modified
into a prehensile organ, the terminal joint folding back upon the greatly dilated pen-
ultimate joint ; last thoracic appendage smaller than the others ; first three pairs of
abdominal appendages natatory, with broad basal and two expanded distal joints fringed
with long plumose hairs ; inner joint of second pair prolonged iu the male into a
penial filament ; fourth and fifth appendages l)rauchial ; sixth pair natatory, compara-
tively small.

External Cliaracters. — The depressed form of the body which characterises the family
of the Isopoda as contrasted vdth. the Amphipoda is very marked in the genus Serolis ; in
some fi])ecies {Serolis schythei, Serolis coriiut<(, &e.) the body is almost flat; in others
again {Serolis convexa, &c.) the convexity of the dorsal surface is greater, and Serolis

8 THE VOYAGE OF H.M.S. CHALLENGE!?.

latifi'ons is conspicuous by its strongly arched dorsal surface, which, together with the
shortness of the e|)imera, causes this species to resemble in general aspect the more
t^i^ical forms of the Cymothoada?.

The outline of the l;»ody varies from oval {Serolis tuberculosa) or even pear-shaped
(Serolis convexa) to circular, and in the males of Serolis schythei and Serolis cormita the
diameter of the body from side to side is somewhat greater than the length.

In the majority of the Isopoda the " head " segments become fused with the first
seo-ment of the thorax, and form a cephalic shield which is freely movable upon the
second thoracic segment. In Serolis the disposition of the anterior segments of the body
differs much from other Isojioda. The first two thoracic segments are closely united and
completely fused dorsally, though the sterna of the two remain distinct ; in some species
[Serolis schythei, Serolis necera, &c.) an incomplete transverse suture upon the first epimera
seems to mark the line of division between the two segments dorsally ; in others again
(Serolis antaretica and all the Australian species) the epimera of the two thoracic
segments are completely united, and show no traces of their original distinctness ; these
epimera are always largely developed, and completely enclose the cephalic shield on both
sides. The cephalic shield is very large and has the form of an heraldic shield ; it is pro-
longed in front into a short rostrum ; its shape varies considerably in the diff'erent
species, in some [Serolis necera, Serolis paradoxa) the antero-lateral portions are consider-
ably expanded, and the transverse diameter is greatest here and decreases posteriorly ;
in other species [Seivlis convexa, Serolis schythei) the cephalic shield is widest at the
level of the ej^es. In the majority of species the cephalic shield is sejiarated from the
two thoracic segments by a continuous suture ; in Serolis longicaudata this suture is
obsolete behind and indicates the commencement of the formation of a cephalothorax
composed of the head segments and the two first thoracic segments as in Tanais, with
which genus Serolis is considered by some to be closely connected. The five following
thoracic segments are free ; the eighth or terminal segment of the thorax differs from
that of other Isopoda in being only represented ventrally by a short sternum, wliich
is more or less intimately fused with that of the preceding segment, and is not prolonged
into epimera ; the tergum of this segment is entirely undeveloped, and the rudimentary
condition of the whole segment (including the appendages, which are much smaller thnn
those of the other thoracic segments) is interesting, inasmuch as in the Isopoda generally
the terminal segment of the thorax is only developed very late.

The epimera of the thoracic segments are almost always largely developed in com-
parison with ntlier Isopoda; and in some of the deep-sea species [Serolis hromleyana,
Serolis necera) are extraordinarily elongated, and terminate in sharp spiniform points. As
a general rule the epimera are flat and sickle-shapt'd, curving back and gradually
increasing in length up to the sixth pair, which are invariably the longest ; sometimes
[Serolis latifrons, Serolis longicaudata, &c.) the epimera are very short, and hardly exceed

EEPORT ON THE ISOPODA. 9

ill leiigtli those of many Cymotlioadse ; where the epimera are only moderately developed
they are in close contact for the greater part of their length, the anterior slightly over-
lapjjing the posterior ; in Sewlis necBva, Serolis hromleijana, and Serolis gracilis the
epimera are quite independent for the greater part of their length, and are only in actual
contact for a short space close to the junction of the epimera and tergum ; at this point
the anterior margin of the epimeron projects forwards as a short rounded process which
is received into a "glenoid" cavity between two similar processes, one dorsal and one
ventral, of the epimeron in front ; of these processes only traces exist in Serolis scliythei
and those species in which the epimera are closely applied to each other ; an intermediate
condition is seen in Serolis paradoxa and other species, where each epimeron has two
articular processes, one anterior and one posterior ; the anterior process of each segment
overlaps the posterior process of the segment in front.

The epimera of the first three free thoracic segments are invarialjly separated from
their terga by a distinct suture ; in some species {Serolis scliythei) the following pair of
epimera are also thus separated ; in Serolis latifrons all the free thoracic segments have
the epimera divided by a suture from the terga.

The abdomen in Seivlis consists of three freely movable segments and a terminal
caudal shield which represents the three posterior appendages of the abdomen together
with the telson.

The anterior segment of the abdomen is enclosed between the penultimate thoracic
and the second abdominal segment, and in one species only has any traces of epimera ;
in Serolis latifrons a minute portion is separated otf from the median portion on either
side by a suture ; and as this suture is quite continuous with those in front which separate
the teroa and sterna of the thoracic segments, it seems that the minute nodule on either side
of the first abdominal segment really represents its epimeron. The two succeeding
segments are always furnished with epimera, which are, however, never se^iarated by a
suture from the terga, and in most cases are short and not prolonged beyond the lateral
margin of the caudal shield ; in some species, notably in Serolis hromleyana, the epimera
of these segments ai'e elongated, and reach midway down the margin of the caudal shield,
or even considerably beyond its termination.

The remaining abdominal seomeuts are fused with the telson to form a caudal shield
which is commonly more or less pentagonal in outline, and is always furnished with a
longitudinal carina and sometimes wth a pair of lateral carinas which appear to mark the
line of di\dsion between the posterior abdominal segment and the telson ; the greater
portion of the caudal shield is occupied by the latter.

Appendages. — The two pairs of antennce are generally subequal in size, sometimes
{e.g., Serolis minuta) the anterior pair, sometimes {e.g., Serolis cornuta) the posterior pair
are the longer.

The anterior antennae consist of four joints and a terminal filament, while the posterior

(ZOOL. CHALL. EXP. — PART XX5III.— 1 884.) Kk 2

10 ■ THE VOYAGE OF H.M.S, CHALLENGER.

antennfB have a stem composed of five separate joints ; tlie terminal filament is usually
shorter than that of the anterior antennae.

Tactile Organs. — The peculiarly modified antennary hairs first described by Leydig/
and believed by him to be sense organs, exist upon the first pair of antennae only in all
the species of Serolis that I have examined. These organs are of two kinds, the most
conspicuous being cylindrical jointed hairs, several of which are displayed in PL I.
fio-. 4, b ; each consists of a basal portion somewhat hour-glass shaped, which is attached
to the inner side of the upper extremity of each of the joints which compose the filament
of the antenuules ; this is continued into a delicate cylinder with thin walls, which is
always divided into two portions by a transverse septixm, and occasionally seems to
consist of three distinctly separated portions ; the distal end of each of these cylinders is
formed by a kuol)-like thickening of the chitinous wall. Leydig describes and figures
nerve fibres and cells in these olfactory hairs, but the Challenger specimens were not
sufiicientl)' well preserved to show these structures.

As a general rule, only one of these olfactory hairs is found upon each joint of the
antennulary filament, but in Serolis antarctica, Serolis australiensis, and one or two
other species, two such hairs are found upon each joint.

The " tactile " organs described by Leydig in the Memoirs already quoted I have only
seen in Serolis schytliei and Serolis necera ; on the antennules of these two species one
tactile hair only is found upon the distal extremity of the terminal point (PI. V.
fig. 5, a) ; it is a short slender hair, the upper half being plumose. Similar hairs are also
found over the general body-surface and upon the first joint of the ambulatory appendages
(PL III. fig. 11) of many species.

The mandihles are very strong and powerful, and furnished with a long three-jointed
palp which is longer than the mandible itself; the second joint of the palj) is longer
than the first joint, and the third, which is very small, is semicircular in shape, and
its flat inner margin is furnished with a row of stiff hairs, of which the two distal
ones are the longest. These hairs are continued for a short way on to the middle joint
of the palp, this part of the joint being of a somewhat greater diameter than the posterior
portion, which is devoid of hairs. The basal portion of the mandible is broadest
proximally, where it articulates with the head, it narrows abruptly into the distal half,
which is not more than one half of its diameter ; the latter is bent at an angle to the basal
part, terminates in the masticatory edge which is of a dark brown colour, and is either
straight or slightly sinuous, or provided with one or two blunt tooth-like projections ; in
adult specimens only are the mandibles thus furnished with a comparatively smooth edge,
Avhich appears simply to be due to wear and tear ; in young specimens of all the species

' Fr. Leydig, Ueber Geruchs- und Gehororgane der Krebse und Insecten, Archivf. Atiat. u. Physiol., 1860, pp. 265-
314, Tafn. vii.-ix See also the same Ueber Amphipoden und Lsopoden, Zcitschr. f. viss. ZooL, Bd. xx.\.. Supplement,
pp. 225-274, Taf. ix.-xii., 1878.

REPORT ON THE ISOPODA. 11

tluit I was able to examine the iuuer edg'e of the mandibles is strongly toothed. Schiijdte,
in a memoir upon the structure of the mouth in the Isopoda,^ has figured and described
the mouth parts of Serolis paradoxa ; the mandibles are distinguished from those of other
Isopoda by their blunt edge, wliieh renders them especially fitted for grinding and not for
tearing, and Schiodte suggests that the food of Serolis jirobably consists of " such animals as
have firm integuments ; " in all the specimens that I have examined the stomach contained
debris of other Crustacea, frequently recognisable fragments of their own species, besides
Diatoms, morsels of the calcareous structure of Echinodermata, &c. ; Schiodte is therefore
quite right in his supposition regarding the food of Serolis, and is no doubt justified in
distinguishing this genus from other Isopoda by the characters of its mouth appendages.

The mandibles of Serolis, however, possess additional cutting blades and spiniform
processes which appear to have been overlooked or imperfectly described and figured liy
all previous writers with the exception of Schiodte. On PI. II. figs. 2, 3 are figured the
distal extremity of both mandibles right and left of Serolis latifrons; the left mandible
has upon the upper surface a triangular chisel-like blade, and below this a long spine ;
the right mandible has the spine, but the cutting 1;)lade is smaller. The left mandible
of other sj)ecies is quite similar to that of Serolis latifrons, but as a general rule
{cf. e.g., fig. of Serolis schythei, PL II. figs. 12, 13) the cutting blade is not present on the
right mandible, its place being occupied by a large spine-like structure. The presence
of these structures appears to me to fit the mandibles for tearing as well as grinding.

The asymmetry of the mandibles is marked not only by the differences just mentioned
l)ut also by the general shape of the masticatory edge {cf. e.g., PI. II. figs. 12, 13) and by
the fact that one mandible, generally the left, is smaller than the other. An asymmetry
(jf the mandibles appears to be a fairly constant character of the Isopoda.

The riiaxillce are small and delicate ; the anterior pair consist of a narrow basal
portion or " cardo," with which is articulated a long flat somewhat curved distal lobe ; the
free edge of this is furnished with a considerable number of strong spines dark yellow in
colour. In some species (e.g., Serolis 'pallida) the lobe of the maxilla is much more bent
upon itself and proportionately shorter. In many species I have observed an additional
lobe, which is situated below the large masticatory lamina articulating with the cardo
(see. PI. V. fig. 14); the presence of this was noticed by Audouin and Milne-Edwards,
but subsequently denied by Grube."

The second pair of maxillaj are smaller and more delicate than the anterior jiair, but
like them consist of a basal portion or " cardo "' and a distal portion, which is divided into
two lobes, the upper of which is again suljdivided ; the two anterior are subequal and
smaller than the posterior lobe, which is separated by a distinct suture ; the free
extremities of all bear a number of hairs more delicate than those on the first maxilla',

1 KriPyer, Nat. Hist. TichsJci:, ser. 3, vol. iv. (ISdO) ; translated in A nn. mtd Mag. Nat. HUt., ser. 4, vol. i. p. 1 ct setp
- Archivf. Naturgese.h ., Jalirg. xli. Bd. i. p. 214.

12 THE VOYAGE OF H.M.S. CHALLENGEE.

and pinnate at their extremity. There are generally two upon each of the smaller anterior
lobes and a greater number upon the posterior lobe ; in a specimen of Serolis cornuta
(c/. PI. I. figs. 9, 10) this pair of maxillae, like the mandibles, was asjTnmetrical on one
side ; each of the two smaller lobes had two long hairs upon its free extremity ; on the
side one of the smaller lobes was markedly larger than the other, and furnished with four
hairs instead of two.

In Serolis convexa the second pair of maxillae differ in that all the three lobes are
approximately of equal size, and all bear a considerable number of hairs (PI. VI. fig. 14).

The maxilUpedes are of considerable size and entirely conceal the subjacent maxillss ;
they are closely approximated in the middle line ; each consists of a squarish basal portion
and a palp ; the basal portion is divided by a transverse suture into two, and each of
these is again divided by a longitudinal suture ; the proximal half or cardo articulates
with both the median (sphenoidal plate) and the lateral portion of the sternum. The
outer half of the distal half or "stipes," which is generally, though not always, completely
separated from the inner " lamina" by a suture, is thin and flat ; the lamina is stout, and
usually furnished on the inner margin with a row of fine hairs ; the upper end invariably
bears two thick spines ; the palp of the maxilla, which consists of three joints, the
middle one the longest, is attached to the lamina about three-quarters of the way down ;
the second and third joints of the palp are furnished with long hairs on the inner side
in all species; the other joints of the maxillipede are sometimes smooth, sometimes
furnished with long hairs, according to the species.

The second thoracic aiypendage {cf. PI. VI. fig. 10) is modified into a prehensile organ,
the penultimate joint is large and swollen, and the terminal joint is recurved and lies
along its inner margin like the blade of a penknife when closed ; the inner margin of the
penultimate joint has a number of peculiarly formed spines, unlike any that are found
elsewhere on the body. Of these there are two kinds which regidarly alternate ; one set
(PL VIII. fig. 15) consist of a central stem terminating above in a knob,^ the margins are
beset with a number of fine branches which are fused together on each side for the
greater part of their length; the other kind of spines (PI. VIII. fig. 14) which alternate
with these, and are placed slightly more on the ventral side, are long and delicate,
expanding above into two processes, one of which is frecj^uently longer and somewhat
spoon-shaped, between these the central axis of the spine terminates in an oval knob ; the
shape of these hairs varies much in the difi"erent species, and will be more fully described
below under the several species.

The fourth joint of this appendage, which is sometimes [Serolis tuhercidata) prolonged
into a forwardly directed triangular process, is always furnished with two spines, and has
in the males of Serolis convexa and Serolis gaudichaudii a tuft of sensory hairs (see p. 17).

The third 'pair of thoracic appendages in the male (see p. 16) is modified into a

* Owing to an error in the plate, this is represented as a forked process.

REPORT ON THE ISOPODA. 13

prehensile organ like the preceding liml), but smaller. In the female it is simihir to the
succeeding appendages.

The remaining thoracic ajij^endages are similar to each other, and are always
furnished with tufts of hairs and spines. The first joint, which is always the longest, is
generally smooth, or provided on the inner surface with fine plumose hairs like the single
sensory hair commonly found upon the terminal point of the filament of the first
antennae. The four following joints are smaller, and generally furnished on the inner and
outer side with tufts of sword-like and of serrated spines. In many species (Serolis
witarctica) these are to a great extent replaced by fine hairs, and in Serolis necera
all the thoracic appendages are clothed with fine plumose hairs similar to those wdiich
in other species are only to be found upon the abdominal appendages. A more detailed
description of the varieties of these hairs and spines will be found under the description
of the several species.'

The last pair of thoracic appendages (see p. 17) are usually smaller, and verj^ often
in the males {Serolis gracilis) furnished on the inner side with tufts of delicate sensory
hairs like those upon the second thoracic appendage in the males of Serolis convexa.

The abdominal appendages [see F\. I. figs. 12-14) are much specialised; the three
anterior pairs form "swimming feet"; each of these consists of a proximal joint, the
protopodite, which is generally triangular in form and attached to the segment which
bears it for about a quarter of the length of the base ; the projecting angle bears three
plumose hairs in the first of these appendages and two in each of the two following. In
some species (viz., Scrolls schjthei, Serolis paradoxa, and in all the Australian species), the
protopodite is narrower, less triangular in form, and has no hairs. The inner margin is
usually clothed with a dense covering of fine delicate hairs, which are also found, though
to a less extent, upon the outer border. About half-way between the summit and the
base the endopodite is attached, and the exopodite at the summit of the protopodite ; both
the exopodite and endopodite are delicate seraicircular lamellfe, the former being larger
than the latter ; the outer convex margin of both is provided with numerous plumose hairs
which, as shown on PI. I. figs. 15, 16, consist of a central hollow stem gradually decreasing
in diameter towards the extremity, and giving off' on either side a series of extremely fine
lamelhe ; in the interior of the stem I was able to observe, in several cases (PI. I. fig. 16),
a fine thread occasionally looped upon itself and possibly a nerve fibre ; the function of
these hairs may perhaps be to test the quality of the water coming to the gills.

The lower border of the endopodite in the second of these appendages is prolonged in
the male into a penial filament (PI. VII. fig. 2', h). The next two pairs of appendages con-
sist of a short basal joint laterally elongated, with which are articulated two broad lamella),
an endopodite and exopodite, which are the gills ; the exopodite of the first appendage is

1 I make an arbitrary distinction here and elsewhere between the finer " hairs " and stouter " spines " in order to
express more easily the differences between the ambulatory appendages of different species.

14 THE VOYAGE OF H.M.S. CHALLENGER.

much stouter than its endopoclite, and forms an "opercuhmi" divided by a transverse
suture, which may be at right angles to the longitudinal axis {Serolis tuherculata, &c.) or
inclined more obliquely to it {Serolis schythei, &c.) ; very commonly (Serolis necura, PL V.
fig. 1 1) the endopodite of this aj^pendage is bifid at the tip, the inner branch being prolonged
beyond the outer ; in most cases, however, the endopodite is entire ; the second pair of
oills is always smaller than the anterior pair, the exopodite and sometimes the endopodite
is divided by a transverse suture which follows the direction of the suture on the exopodite
of the first pair of gills. The terminal appendages of the abdomen or " uropoda " are
always comparatively small ; in Serolis antarctica they are extremely minute ; these
appendages consist of a triangular basal joint attached by the apex to a notch on the
lateral margin of the caudal shield, which varies in j)osition in difi'erent species, being
sometimes at the anterior end of the lateral margin of the caudal shield, sometimes close
to its posterior extremity ; the inner angle of the protopodite is always longer than the
outer, and the endopodite is longer than the exopodite; in Serolis latifrons Studer^ has
correctly described the elongated and spine-like endojjodite which becomes completely
fused with the protopodite, while the exopodite remain very short ; the appendage is
capable of lieiug flexed at right angles to the body, and its sharp spiniform character
doubtless serves as a protection against many foes.

Sexual Characters. — The generative apertures of the male are always situated on the
last thoracic segment, on either side of the median ventral line they are always closely
approximated, but difier slightly in difi'erent species; in some {e.g., Serolis antarctica)
they are so close together as almost to form a single orifice ; in others {Serolis schythei,
&c.) they are a little further apart.

The female generative apertures are more widely separated from each other than the
male generative apertures; they are situated on the antepenultimate thoracic segment, and
have the form of an oval slit, while the male generative apertures are invariably cii'cular.
The ova are carried about by the female until the young are fully formed ; the
immature females have four ovigerous lamellae (see PI. V. fig. 4) developed on the second to
the fifth thoracic segments inclusive, which are short, oval in shape, and attached close to
the attachment of the thoracic limbs. Studer ^ was the first to point out that these lamellae
become much larger in the mature females with eggs, and overlap each other in the
middle line, those on the right generally covering those on the left ; this disposition of
the ovigerous lamellae, though general, is not, however, universal ; occasionally {e.g., Serolis
Gonvexa) the arrangement of the lamellae alternates, the right hand lamella3 of the second
segment overlapping that of the left ; in the two succeeding segments the left hand lamellje
overlaps the right, and finally the disposition of the lamellae in the fourth segment is like
that in the second. These cases appear, however, to be irregular, and not to be char-
acteristic of difi'erent species. When these brood lamelte are fully developed the sterna

' Archivf. Natunjesch., 1879, loc. cit. 2 Loc. cit, p. 20.

REPORT ON THE ISOPODA. 15

of tlio thoracic segments undergo a retrograde development and almost disappear, and the
animal does not appear to take any nourishment ; in all the mature females that I have
examined the young appear to be actually contained within the body of the mother, the
alimentary canal is pressed up against the dorsal surface of the body, and its cavity is
reduced to a minimum ; a delicate chitinous membrane is all that remains of the
thoracic sterna.

Secondary Sexual Characters. — The males of SeroUs also diifer from the females
in a number of secondary sexual characters, which may be divided into two groups —
(l) those which are common to all the species of the genus, (2) certain other characters
which are confined to one or more species.

1. As a general rule the males of Serolis are somewhat larger than the females ;
this is certainly the case with Serolis bromlei/ana and Seivlis necera, in which species
the males are not only longer but also broader, owing chiefly to the greater development
of the spine-like epimera so characteristic of these two species. In Serolis cornuta,
Serolis schijthei, and Serolis latifrons the difierence in length l)etween the two sexes does
not appear to be great, but the males are considerably broader than the females; especially
is this so in Serolis schytliei, where the proportion between length and breadth is almost
reversed in the two sexes ; in the male the breadth is greater than the length, in the
female, on the contrary, the length is greater than the breadth, and the difierence between
these two dimensions is very near to being the same in both sexes. In Serolis antarctica
and Serolis gracilis the males have a greater antero-j)osterior as well as transverse
diameter than the females.

Among the Australian species, on the contrary, the females appear to be larger than
the males, but since the number of specimens in each case was extremely small, it is
impossible to speak with certainty. Of Serolis aiist7-aliensis two out of the three speci-
mens are males and smaller than the single female specimen ; of Serolis tiiberculata the
Challenger obtained two specimens, one of each sex, and here again the male is the
smaller ; the male specimen also which has been described l)y Grube ^ is of aliout the
same size as the male which I have examined ; finally, in the only other Australian species,
Serolis j^nlJida, of which more than a single example was obtained by the Challenger,
the female is larger than the male.

In the majority of species of Serolis tliere is a difference in the length of the epimera
in the two sexes, and this difference is most .strikingly shown in Serolis (jracilis; in the
males of this species the epimera gradually increase up to the sixth, the last thoracic
epimera, which are enormously elongated and extend beyond the termination of the
caudal shield for a considerable distance.

In the female the epimera are very much reduced in size ; the sixth pair, instead of
being prolonged beyond the caudal shield, do not reach as far as its extremity.

' Lor. cit., p. 227.

16 THE VOYAGE OF H.M.S. CHALLENGER.

In most other species the same conditions occur, and a comparison in detail of the
posterior epimera, which difler more in length in the two sexes than the epimera of the
anterior segments, will be found under the description of species.

Some few species do not show these differences; in Serolis paradoxa, for example, the
males, on a superficial view, are indistinguishable from the females, and the difference in
size between the two sexes is hardly if at all marked.

As a general rule the sterna of the three anterior abdominal segments serve to
distinguish the sex of the individual ; in the females the middle portion is commonly
prolonged into a stout spine, while in the males this structure is not present, and
the posterior margin of the segments is straight or slightly concave. In a great
number of species, however, the two sexes do not differ at all in this way.

Another marked secondary sexual character, which is quite univei^sal in the form of
the third thoracic appendages ; in the females this pair of appendages is entirely similar
to the succeeding ambulatory limbs ; in the males, on the contrary, the penultimate joint
is swollen and furnished on the inner side wdth a number of peculiar modified spines,
the terminal joint is recurved, and the appendage thus forms a prehensile organ very
like the second thoracic appendage. Of Serolis tuherculata Grube states {loc. cit.,
p. 230) — " Die Fiisse des 2'™ Fusspaares sind weniger ausgepriigte Greiffiisse als bei
andern Arten ; zwar zeichnet sich das 3'* und 4"^ Glied durch seine Kiirze vor den ent-
sprechenden der folgenden Beine aus, aUein das Handglied ist weniger breit als sonst, sein
Innem-and nicht liings der ganzen Schneide mit Ziihnen besetzt, und die Klaue scheint
nicht so zum einschlagen geeionet zu sein. Die Ziihne sind ziemlich lanof und stachel-
formig mit einer Andeutung von Nebenzacken." The male specimen of this species
which I have examined myself does indeed display such differences from the ordinary
structure of these appendages in all other Serolis as Grube describes ; both
specimens are, however, evidently immature ; the characters that he mentions exactly
correspond to the appendages of immature males (see infra, p. 27).

These appendages are used liy the male during coj)ulation ; the claw is firmly
imbedded in the epimera of the female, so firmly that the individuals can hardly Ix;
separated without injury.^

In all species of Serolis, as in many other Isopoda, the second pair of abdominal
appendages bear a long penial filament ; these are a continuation of the lower margin
of the eudopodite of the limb, and reach in some cases as far back as the end of the
caudal shield ; in other species they are not quite so long. The end of these filaments is
blunt and rounded, and not furnished with any aperture ; it seems possible for this reason
that the two are approximated during copulation, and form a groove down which the
spermatophores pass ; the fact of the male generative apertures being placed so closely
together seems to favour this supposition.

' StuJtr, Isopoden gesammelt wakreud der Reise, &c., loc. cit.

REPORT ON THE ISOPODA. 17

lu the females there is no trace whatever of these penial filaments.

2. Under this head I may briefly review certain outward ditferences in male and
female individuals which are peculiar to one or more species, and of which a fuller
description is given below.

In Serolis convexa (PI. VI. fig. 10) and Serolis gaudichaudii the second pair of
thoracic appendages in the male are furnished with a tuft of pinnate hairs upon the
inner side of the antepenultimate joint, and in the male of the former species, at any rate,
the sterna of certain of the thoracic segments are provided with patches of similar hairs.

In Serolis septemcarinata the epiraera of the males bear a row of five or six elongated
ridge-like tentacles on the under surface which are entirely wanting in the female.

The females of Serolis nexera are distinguished from the males by the fiir greater
development of the frontal "sense organ"^ {cf. PL V. figs. 1, 3), and the epimera them-
selves show certain difi'erences in the two sexes, being considerably wider in the male,
where the anterior margin from the point of junction with the lateral angle of the
cephalic shield slopes gradually backwards and outwards to the termination of the
epimeron ; in the females the anterior margin passes at first directly backwards almost
parallel to the longitudinal axis of the body, and then slopes outwards so that in this
sex the anterior epimera look as if a piece had been cut out.

Another sexual diff"erence is found in Serolis gracilis and Serolis convexa, and is men-
tioned by Audouin and Milne-Edwards as occurring in Serolis gaudichaudii^^ In these
species the terminal thoracic appendages of the males are beset with fine hairs, which are
similar in shape to the hairs upon the second thoracic appendages of the males of Serolis
convexa and Serolis gaudichaudii; these same appendages in the females do not difi'er in
any way from the preceding thoracic appendages.

On PL II. fig. 6 is figured a single joint from the filament of the second antenna
of a male Se^'olis scliythei ; along the inner margin of the joint are a series of delicate
fan-shaped lameUse which I did not succeed in finding in any female example of this
species; it is possible, however, that on account of theii- extreme delicacy they may have
been overlooked.

Alimentary Canal. — The alimentary canal of Serolis agrees closely with that of other
Isopoda; the point to which I may call special attention is the presence of salivary glands,
which I have noticed in Serolis ixtradoxa and Serolis septemcarinata. On account of

' Grube was tlie first to point out the presence of a transparent oval area on the first epimera wliich he imagined
might cover some sense organ ; Dr. Woodward (Geol. May., 1883, p. 21) has compared this structure to certain pores
which are to be found in many Trilobites occupying an identical position. I have foimd that this structure exists in
nearly all the species of Serolis, generally having the form of a deep and narrow groove surrounded by a specially
thickened rim; in SerolU schytlwi and Serolis cornuta the structure is precisely as described by Grube in Serolis paradoxa,
and as in that species there is a jiore on the under surface of the epimeron exactly beneath it. In Serolis antardica and
others I could discover no trace of it. Concerning the minute anatomy of this " sense organ," I am unfortunately able
to say nothing.

^ Loc. cit., p. 19.

(ZOOL. CHALL. EXP. PART XXXIII. — 1884.) Kk 3

18 THE VOYAGE OF H.M.S. CHALLENGER.

its conveniently small size I selected the latter species for anatomical study by means of
transverse sections, which I found much better than dissection owing to the state of
preservation of the specimens.

On PI. X. fig. 6 is figured a transverse section through the head of Sei'olis septem-
carinata showing the salivary glands in situ; a is the aperture of the mouth, h the buccal
cavity, and c points to the ventral wall of the body bounding the mouth ; the salivary
glands [d) are arranged in rosette-shaped aggregations of cells surrounding a central
cavity ; these cells are highly granular, and stain deeply with carmine ; each is j^rovided
with a large nucleus which stains rather more deeply than the surrounding protoplasm ;
the glands are imbedded in the cellular connective tissue of the body, some of the cells
of which are shown in the figure (e). Similar structures have been observed by Dohrn ^
in Anceus and Parantliura, and are figured and described by him in his account of the
anatomy of these two genera.

The oesophagus, as in other Crustacea, passes upwards into the masticatory stomach,
which is furnished with a complicated series of chitinous plates.

On PI. X. fig. 9 is figured the masticatory stomach of Serolis hromleyana viewed from
beneath ; the " pyloric "end is directed towards the upper margin of the plate.

There is an ujjper median azygos cardiac plate {m) ; in front of this and below is a
cylindrical plate (LR, RP) on either side ("Eeibe-platte"), the lower surface of which is
traversed by a row of rib-like thickenings. On either side of the median plate are three
lateral plates {I, la, Ijj), one median, one anterior, and one posterior ; the median lateral
plate (I) is furnished with numerous fine hair-like processes on the under surface. On
the ventral surface of the stomach is a large ossicle ( F) which reaches beyond the
commencement of the dorsal azygos piece (wi), and terminates in a bifurcate extremity ;
behind this comes the j^yloric portion of the stomach, which has four ossicles on either
side; two small triangular ossicles (t), situated just above the median piece (F), and
behind three pairs of elongated ossicles which are furnished with delicate hairs directed
inwards and form a sieve-like structure ; the outermost ossicle (2) is connected both with
the median ventral ossicle ( F) and the lateral plate (R-P.) of its own side ; s points to the
pyloric^aperture.

In Serolis antarctica the masticatory stomach is entirely similar.
• In Serolis ixiradoxa the masticatory stomach apparently differs from that which has
just been described by the very incomplete calcification of the cardiac ossicle, which is
indeed hardly to be recognised as a distinct ossicle ; the ventral median ossicle does
not extend so far backwards as in Serolis hromleyana, and is less markedly emarginate
at its apex.

The masticatory stomach in the two other species in which I have studied it, viz.,

1 Entwickelunr; und Organisation von Praniza (Anceu.s) uiaxillaris, Zcitschr. f. wiss. ZooL, Bd. xx. p. 55, 1870 ; and
also Zur Kenntniss des Baues von Paruuthura cos^taua, Ibid., p. 81.

REPORT ON THE ISOPODA. 19

Serolis schijthei aud Serolis latifrons, presents some differences. Fig. 4 is a drawing of
the masticatory stomach of Serolis schythei, which is entirely similar to that of Serolis
latifrons; the chief difference from Serolis hromleyana is that the lateral ossicle (fig. 4, 1)
is furnished upon the upper surface with short spines in addition to the delicate hairs
which clotlie its lower surface. The outermost of the three pairs of ossicles which form
the pyloric half of the stomach is also more extensive, and bears the ribbed lateral plates
{RP, LP) upon the anterior edge.

At the junction of the masticatory stomach with the intestine are four caeca which
are long and coiled in Serolis cornuta (PI. X. fig. 2); in a specimen of Serolis
necBra that I dissected there were also four cseca, two situated beneath the gut, and con-
siderably shorter than the other two which lay along the outer margin.

From the masticatory stomach arises the intestine, which is at first wide but gradually
narrows towards the rectum ; the latter commences at about the level of the fifth
thoracic segment, and is separated off from the intestine by an incomplete circular valve ;
the anus is an oval aperture ou the ventral surface of the body between the attachments
of the gill plates. The intestine as well as the rectum is provided internally with a
series of lonoitudinal oiandular folds.

In a member of small specimens of Serolis latifrons mounted on slides in Canada
balsam the alimentary canal was distinctly visible ; between the wdde anterior portion
of the intestine aud the rectum, which is half its diameter, is a narrow portion of the gut,
measuring at its commencement rather less than one half of the diameter of the rectum,
and then becoming slightly wider as it approaches the latter.

Nervous System. — The nervous system of Serolis paradoxa is figured in Packard's
Zoology ; ^ Studer has also given a figure and description of the nervous system of
Serolis latifrons; the former of these two figures appears to represent more strikingly
the concentration of the posterior ganglia into a nervous mass where the commissures
and connectives between the several ganglia are lost.

I have studied the nervous system of the genus in two species — in young examples
of Serolis earinata by means of sections and by simple inspection of the entire animal
mounted in glycerin ; in Serolis necera by dissection.

The nervous system of both these species, as in other Crustacea, shows a relation to
the segmentation of the body ; the fusion of the anterior segments is accompanied by a
fusion of their ganglia, and the same thing has taken place in the posterior region of the
body. On PI. II. fig. 1 4 is represented the nervous system of Serolis septemcarinata ;
the drawing has been made from a specimen mounted on a slide, but the number of the
ganglia has been checked by comparison with a complete series of longitudinal sections
through an animal of the same size.

The cerebral ganglia are very large, and present the appearance of being composed

1 Zoology, Packard, iud ed., New York, 18S0, p. 307.

20 THE VOYAGE OF H.M.S. CHALLENGER.

of a number of separate lobes ; a paii- of conuectives unite the cerebral ganglia with
tlie ventral chain ; the latter is composed of thirteen distinct pairs of ganglia, some of
wliich bear unmistakable evidence of being the result of a fusion between several pairs
of primitively distinct ganglia ; this is particularly the case with the anterior of the
ganglia, which are seen in longitudinal section to be composed of two fused ganglia.
The eight following ganglia belong apparently to the thorax. Of these the three anterior ^
are separated from each other by considerably longer connectives than those which
unite the posterior thoracic ganglia ; the latter get closer and closer together (in
correspondence with the diminished size of the segments to which they belong), and
the last pair of thoracic ganglia are hardly separated from the fused ganglionic mass
belonging to the abdomen ; a careful examination of the latter, especially by the help of
longitudinal sections, shows that it is in reality composed of six pairs of distinct ganglia,
the last of which is considerably larger than the rest, inasmuch as it has to supply the
telson as well as the last abdominal segment. The abdominal ganglia occupy only the
first three segments of the abdomen.

In Serolis necera the fusion of the posterior and of the anterior ganglia is even more
marked.

In the cephalothorax there are three pairs of ganglia, of which the posterior is much
the largest. This is united by a long connective with the next thoracic ganglia, which is
situated at the posterior extremity of the second free thoracic segment ; it is clear, how-
ever, that it belongs to the segment in front, since it was quite easy to trace the nerves
passing forwards to this segment. The fourth thoracic ganglion is closely connected
with the succeeding thoracic and the abdominal ganglia, the whole forming an elongated
oval mass lying in the posterior thoracic and anterior ten abdominal segments ; the
demarcations between the four anterior pairs of ganglia could be recognised by the stout
nerves given off on either side to their respective segments ; of the posterior ganglia,
however, it was impossible to discover how many there were ; a vast number of nerve
filaments take their origin on either side, and afford no indication of the number of
ganglia, two of these passing in a direction parallel to the longitudinal axis of the body
from the hinder end of the ventral chain are especially large ; they supply the telson.

Eye. — With one exception — Serolis antarctica, which is perfectly blind — all the
known species of Serolis are provided with a pair of eyes situated upon each side of
the cephalic shield at al)out the middle of its antero-posterior diameter ; the eye has
usually a reuiform outline, and in general aspect recalls that of the TrUobite, with which
it has been compared ; more rarely it is oval {Serolis hromleyana), and in Serolis minuta
it is almost circular.

In all the shallow-water species the eye is relatively small, Ijut very conspicuous from
the abundant deposition of pigment ; in all the deep-sea forms, with the exception of

' This is not clearly shown in the figure owing to an oversight.

REPORT OX THE ISOPODA. 21

Serohs gracilis, iu wliich species the eye seems to be disappearing (see p. 24), it
is relatively larger but not so conspicuous, owing to the fact that little or no pigment is
present ; these external points of difference between the eyes of the deep-sea and shallow-
water species are accompanied by very striking differences in their minute structure.
Since, however, the shallow-water species agree more closely with other Ai-thropoda in
the structure of the eye, it will be more convenient to commence with them before
describing in greater detail the deep-sea species.

Among the shallow-water species I have investigated the minute structure of the eye
in the following: — Scrolis schythei, Serolis paradoxa, Serolis latifrons, and Senilis cor-
nuta. In all there is a fundamental similarity, Ijut there are certain differences in detail.

In Serolis schythei the eye (PI. IX. fig. 2) is facetted externally, and a transverse
section shows that each facet forms a doubly convex lens, the posterior convexity beino-
more marked than the anterior. Corresponding to each lens is a vitreous body (i-) of an
oval conical form, and composed, as in other Isopods, of two halves joined in the middle
line ; as a general rule the vitreous bodies have the even regular form displayed in the
figure, but some are uneven, one half being larger than the other; surrounding the vitreous
body are the remains of the two cells which gave rise to them, and above, between the
vitreous body and the cornea, are two nuclei (" nuclei of Semjjcr ") which belong to
these cells. The whole " vitrella "^ is enclosed in a sheath of deep black pigment cells.

Below the vitrella is the retinula, which consists of only four cells ; this is an un-
usually small number ; from Grenacher's work upon the Arthropod eye already quoted,
it appears that five or seven cells is the usual number, aud in some cases the retinula
contains a greater number of cells ; Gammarus locusta would seem to be the only known
Crustacean besides Serolis in which the retinula is composed of so few as four elements.
Each of the retinula cells is club-shaped when viewed in front (fig. 2) ; seen laterally they
are hatchet-shaped (figs. 18, 19); at about the middle of the cell is an oval swelling
where the nucleus is situated ; the nucleus is oval iu form, the long axis corresponding
to the long axis of the cell, and is contained in a cavity ; in the interior of each nucleus
is a small highly refracting nucleolus. The retinula cells arc clothed externally -nith a
coating of pigment, which is more especially developed at the upper swollen extremity
and gradually decreases in amount towards the lower end ; this pigment apj)ears to be
contained in long branched connective tissue cells. The retinal cells themselves, however,
do contain intrinsic pigment iu addition to this adventitious sheath, as is shown by
transverse sections. Fig. 20 represents a series of sections through a single retinula at
various points which are indicated iu the description of plates ; from these sections it
may be seen that the retinal cells contain abundant pigment granules within their own

^ The nomenclature used in this description is taken from Grenacher's Untersuchungen iiber das Sehorgan der
Arthropoden, Gcittingen, 1879; and from a Jlemoir on the Eyes of Limidus and Scorpio by Prof Lankester and
Mr. A. G. Bourne {Quart. Journ. Micr. Sci., N. S., vol. xxiii. p. 177, 18S3).

2-2 THE VOYAGE OF H.M.S. CHALLENGEK.

substance, especially towards the circumference. The nuclei of the pigment cells become
conspicuous in teased preparations of the eye depigmented by means of nitric acid.

At the upper extremity of each retinula cell, and lying upon the inner margin, is a
clear chitinous rod, the " rhabdomere " (fig. 18, r) ; the four rhabdomeres are more or less
closely united to form the rhabdom, which is shown infigs. 2, 5,r ; the lower extremity of the
rhabdom is produced into a fine thread, reaching nearly as far as the pigmented membrane
which bounds the inner surface of the eye. Below this membrane, which is of some
thickness and pigmented only upon its upper surface, the retinal cells are continued into
stout nervous rods which are .slightly swollen at the upper end, where they come into
contact with the retinal cells.

The pigment sheath of the retinal cells is continued for a short distance along the
nerve rods ; the latter exhibit transverse markings, and are a little like striated muscular
fibres ; it is very likely that these structures in other Crustacea have contributed to the
erroneous idea that the Arthropod eye possesses intrinsic muscular fibres serving as a
focusing apparatus. It has, however, been clearly shown by several investigators that
there are no such muscular fibres present.

So far the eye of Serolis schythei only differs from that of other Isopoda in unim-
portant details. I now proceed to describe another structure which enters into the com-
position of the eye in all the species of Serolis that I have examined, but which has not to
my knowledge been figured or described as occurring in the eye of any other Arthropod ;
this structure consists of two large hyaline bodies situated below the rhabdom, and enclosed
by the upper extremities of the four retinal cells (fig. 2, h). Occasionally only one seems to
be present in a single retinula, and very often the size of the two is unequal, one being
considerably larger than the other (fig. 10). Each of these bodies is clear and transparent,
the substance of which it is composed having very much the appearance of chitin, and I
was at first inclined to think that the whole structure in all pioljability represented the
rhabdom of other Arthropod eyes. Seeing, however, that a rhabdom is present — though
rather small and inconspicuous — this comparison cannot hold good, and moreover each of
these hyaline bodies shows an irregularly shaped granular mass, deeply stained by carmine
and other reagents, which would seem to be a nucleus ; it is evidently therefore an indepen-
dent structure and not a product of the retinal cells ; the lower end of the rhabdom is
imbedded in these two cells, and the filiform prolongation of the same appears to pass
through their substance. The large size and transparency of these hyaline cells seems to
indicate that they serve as a dioptric medium. I am not able to say whether these
structures represent highly modified retinula cells or intrusive connective tissue cells,
inasmuch as 1 have found them already well-developed in the youngest specimens that I
have examined.

In Serolis paradoxa the structure of the eye is in most respects similar, but each of
the cells which compose the retinula secretes in addition to the rhabdomere a small highly

REPORT ON THE ISOPODA. 23

refractive lens-like body or " phaosphere." The shape of these bodies as well as their
position varies considerably ; sometimes they are quite spherical, occasionally they are
oval, and more rarely bean-shaped ; they are more usually found in front of the nucleus
of the retinula cell, sometimes within its swollen anterior extremity ; often they lie behind
the nucleus, and in a few cases they were observed in close contact to the nucleus and
slightly to one side. The phaospheres of all the four cells of a single retinula in some
instances occupied an approximately similar position, though more generally this was not so.

I only succeeded in making out these structures in SeroUs iKiradoxa ; in Serolis
schythei and Serolis com uta they appear to be absent.

Serolis cornuta. — In this species the cells composing the retinula are longer and
more slender than in Serolis schythei or Serolis paradoxa, and the pigment upon their
outer surface is comparatively feebly developed, being chiefly massed round the rhabdom ;
in other respects their structure is similar, and very thin longitudinal sections show that
intrinsic pigment is present within the cells themselves in addition to the intrusive
pigmentiferous connective tissue corpuscles which clothe them externally. The rhabdom
is a remarkably complicated structure, and differs greatly from the simple rhabdom found
in the two species just described. It is displayed in figs. 3, 9-15, which have been
drawn from preparations teased out in glycerin after having been depigmented by means
of nitric acid and in figs. 7, 8, 16, 17, which rej)resent longitudinal sections of this
portion of the eye undepigmented. In the latter the rhabdom is seen to consist of a
number of coiled threads running in various directions and coated externally with a thick
layer of black pigment. The lower extremity of the rhabdom projects into the " hyaline
cells" and is surrounded by their substance. In fig. 4 is displayed a teased preparation
of the eye of Scrolls cornuta undepigmented, and it may be seen that the rhabdom ends
below in blunt rounded prolongations which project into the "hyaline cells"; the lower
extremity of each of these prolongations — which indicate the composition of the rhabdom
out of four rhabdomeres^is devoid of pigment, so that the rays of light can pass through.
In longitudinal sections of course only one or two of these can be seen, though there are
in reality four.

The shape of the rhabdom can best be made out by teased depigmented preparations ;
fig. 3 represents a single retinula prepared in this way ; the rhabdom is here seen in
profile and resembles an irregular coil of rope projecting below into the hya^line cells
(//) and continued into a thin filamentous prolongation which appears to pass through the
substance of these cells or between them, and extends nearly as far as the lower end of
the retinula cells. Figs. 9-15 represent the rhabdom and the two hyaline cells viewed
in such a position as to bring out the symmetrical character of the former. The form of
the rhabdom, however, differs widely in detail; some of the varieties are displayed in
these figures ; in all it appears to consist of a median unpaired portion which is continu-
ous below with four symmetrically arranged portions which project into the substance

24 THE VOYAGE OF H.M.S. CHALLENGER.

of the two hyaline cells ; the median portion is usually formed by a sinuous rod of vary-
ino- lenfTth which ramifies at its lower extremity into four coils; the whole structure
reminds one very forcibly of the Malpighian bodies of the kidney ; m some cases the
median rod is double, and more rarely (fig. 13) it is represented by four or five pieces;
it is possible that these varieties correspond to stages in growth, the more complicated
{e.g., figs. 11-13) being the older.

The "hyaline cells," as already mentioned, are two in number in each retinula ; the
nucleus is situated close to the lower extremity ; in sections which have been slightly
depigmented the whole of these hyaline cells becomes tinged of a light mahogany brown,
Avith the exception of the nucleus, which remains unstained, and is therefore exceedingly
conspicuous ; in, e.g., figs. 16, 17, which are drawn from such sections, it may be seen that
these cells enclose almost the whole of the rhabdom, and this would seem to suggest that
they are concerned in its production and may therefore perhaps be modified retinula cells ;
the cells themselves are quite homogeneous and transparent — apart, of course, from the
nucleus — and in section appear exactly similar to the vitreous body ; they are, however,
more transparent and quite colourless, whereas the vitreous body is always of a chitin-yellow
colour. In a teased preparation of the eye of Serolis cornuta the addition of strong
nitric acid dissolves out the pigment, which is at first absorbed by the hyaline cells,
causing them to assume a very remarkable appearance, represented in PI. X. fig. 1 ; these
cells become quite granular with a crenated outer margin and of a dark greyish-black
colour ; when the process of depigmentation has gone on a little further the pigment is
dissolved out of the hyaline cells, leaving them perfectly tran.sparent and smooth, or at
most with a slight mahogany brown tinge.

Among the deep-sea species of Serolis the eye is entirely absent in Serolis antarctica ;
its place, however, is occupied by a small tubercle not more than 1 mm. in extent, on
either side of the cephalic shield ; the posterior border of the latter in consequence is
more regular, and the postero-lateral projections which correspond to the eyes are but
slightly marked ; the two tubercles have the same microscopic structure as the rest of
the chitinous integument, and show no traces of facets ; their interior is filled with a plug
of connective tissue, in which no vitreous bodies or retinal elements could be detected.
In Serolis gracilis, another deep-sea form, the eyes present some curious peculiarities.
In two specimens the eyes are well developed, though small, and resemble entirely
the eyes of Serolis hromleyana ; they are conspicuous from their whitish colour,
which contrasts with the surrounding integument ; in one specimen the ocular protu-
berance is only partly occupied by the optic tissues, the rest being exactly similar in
colour to the general integument of the body ; in another sjjecimen there is no trace
whatever of any optic structures, though the oval-shaped elevations of the eye are present
l)ut dark bluish in colour like the rest of the integument. In this species, therefore, the
eye seems to be just on the verge of disappearance.

REPOET ON THE ISOPODA. 25

SvroUs Iromknjana. — That portion of the chitiuous integument that covers the eye
is modified and differs from the rest by its comparative thinness, and l^y the absence of the
characteristic scale-like sculpturing ; corresponding to each element of the eye is a thicken-
ing of the cornea, which is, however, very slightly developed in comparison with other
species, and indeed the two surfaces of the cornea appear in transverse section to form two
nearly straight parallel lines, the lower surface alone showing a series of undulations of
unequal extent. PI. X. fig. 5, and PI. IX. fig. 2, represent transverse sections through
the cornea of Serolls hromleijana and Serolis schythei respectively; the conspicuous
corneal lenses of the latter type are in very marked contrast to the feeble indications
of these structures in Serolis hroinleyana.

The tissues of the eye itself have evidently undergone considerable degeneration, and
this, coupled with the fact that the specimens were by no means well preserved, renders
any satisfactory comparison of their structure with that of the shallow-water species of
Serolis and the Arthropoda generally extremely difficult. I describe the facts as they
appear to me.

PL X. fig. 5 is a diagrammatic representation of a transverse section through the eye ;
beneath the cornea are a series of more or less cup-shaped masses of unequal size and of
a granular appearance ; occasionally several of these bodies appeared to have become fused
together at their upper extremity, and in a few instances a short upward prolongation of
the subjacent tissue into the substance of the body gave it the appearance of being
originally formed out of two separate halves ; the granular yellowish coloured matter of
which these structures consist is almost entirely unaflected by carmine, which stains deeply
the surrounding tissues, and is only slightly stained by hematoxylin. In teased pre-
parations of the eye these structures are easily separated, and are seen to have an oval
contour ; from their position they would appear to correspond to the vitreous body, and
in their general characters recall the vitreous bodies of the type of eye termed by
Grenacher " pseudoconous." The compound eyes of the Arthropoda have been arranged
by Grenacher' into three groups— (1) euconous eyes, (2) aconous eyes, and (3) pseudo-
conous eyes. In the first group the cells lying behind the facets secrete in addition to
it a highly refractive vitreous body or " Kristallkegel," which is composed of as many
segments as there are cells ; in the second group the cells remain unaltered and secrete
no vitreous body; in the third group these cells secrete "a soft fluid or semifluid
substance " which represents functionally the vitreous body of euconous eyes. It seems
to me very possible that the granular appearance of the vitreous body in the deep-sea
Serolis has been caused by the coagulation (by alcohol) of a semifluid substance.
Pseudoconous eyes, which according to Grenacher are only to be found in the order
Diptera, are further distinguished from euconous eyes by the fact that the nuclei of
the cells of the vitreous body (the so-called "nuclei of Semper") remain below the

> Seliorgan iler Artliropoden, Gottingeii, 1879.
(ZOOL. CHALL. EXP. — FART XXXIII. — 1884.) '^^ ^

26 THE VOYAGE OF H.M.S. CHALLENGEE.

vitreous body itself, instead of being placed above it and in close proximity to the
cornea.

1 was unable to detect with certainty these nuclei of Semper in the eye of SerolLs
hromleyaua, l)ut in another deep-sea form, Serolis neoera, having an eye of similar
structure they were very conspicuous, and situated above the "vitreous body" between
it and the cornea. Each of the vitreous bodies of Serolis hromleyana is enclosed in a
cup-shaped sheath of tissue (PL X. fig. 5) in which no trace whatever of any structure could
be made out. This sheath possibly corresponds to the pigment sheath which encloses the
vitreous body in other Arthropoda, but in Serolis hromleyana it is entirely free from
jjigment. Below this portion of the eye, and corresponding to each of the vitreous
lenses, is a roundish mass of cells which are separated into groups by ramifying trabeculse
of pigmented connective tissue ; from the posterior end of this mass of cells a delicate
bundle of nerve fibres arises which passes back to the ganglion ; it is clothed externally
by a layer of pigmentiferous ramified cells continuous with those in front.

The eyes of Serolis necera resemble in external characters the eyes in the shallow-
water species of Serolis; they are distinctly faceted, and a great deal of pigment is present ;
they are also proportionately larger than in any of the shallow-water species.

The minute structure, however (fig. 3), agrees in the main with that of Serolis hrom-
leyana, but is a little less degenerated ; the cornea, as already stated, is distinctly faceted ;
beneath each facet are two large and conspicuous nuclei ("nuclei of Semper"), these are
round or oval, sometimes pear-shaped ; they are surrounded by a distinct membrane
showing a double contour, and contain a highly refractive nucleolus. The vitreous
bodies, like those of Serolis hromleyana, are of an irregular oval form and granular opaque
consistency ; the upper half is encircled by a ring of pigment. At the lower end of each
is a roundish mass of small nucleated cells (g), probably nerve cells, and these are con-
nected posteriorly with a nerve bundle, partly sheathed with pigment cells, which extends
into the mass of nerve cells dividing it up into lobules. Fig. 8 is a single element isolated
by teasing in glycerin ; the vitreous body (F) is very distinctly cup-shaped.

The results of my investigations into the minute structure of the eye in Serolis may
be briefly summed up as follows : — (l) The shallow-water species invariably possess w^ell-
developed eyes which are fundamentally similar to those of other Isopoda, but diflFer
in several particulars ; the retinulse are composed of only four cells ; the rhabdom is
often a highly complicated structure unlike that of other Crustacea. Another element
unrepresented (?) in the eyes of other Crustacea is present, consisting of two large
hyaline nucleated cells placed below the rhabdom and between the retinal cells. (2)
In the deep-sea species the eyes are either altogether absent {Serolis antarctica),
or, if present, show signs of structural degeneration ; no retinula, at least nothing
comparable to the retinula in the eyes of the shallow-water species, is present, but the
vitreous body is represented. The vitreous bodies may be enclosed in a sheath of

REPORT ON THE ISOPODA. 27

pigment {Serohs necera), or there may be no pigment present {Serolis graciUs, Serolis
hromleyana).

Developvient. — Several of the species of Serolis contained eggs within the lirood
cavity in various stages of development, and although these embryos were not sufficiently
well preserved to admit of any examination by means of sections, I have been able to
note down some developmental facts which have an important Ijearing upon the affinities
of the genus. The development history of Serolis, so for as I have been able to trace it,
is strikingly similar to that of the Cymothoada^, which has recently Ijeen worked out in
detad by Mr. J. F. BuUar.' The Lsopoda generally diifer from the Amphipoda in that
the embryo has a dorsal flexure in the former group and a ventral flexure in the latter.
Thus Fritz Muller (Facts for Darwin, p. 71) says — "The curvature of the embryo
upwards instead of downwards was met with by me as well as by Eathke in Idothea
and likewise in Cassidina, Philoscia, Tanais, and the Bop}T.'id8e ; indeed I failed to
find it in none of the Isopoda examined by me." And at p. 74 — "The Amphipoda
are distinguished at an early period in the egg by the diflerent position of the embryo,
the hinder extremity of which is bent downwards." In the C}Tnothoadas — at least in
those species which are treated of by Bullar in the paper from which tlie above quotation
has been made — the embryo is intermediate between the typical Isopoda on the one hand
and the Amphipoda on the other ; it only occupies the ventral surface of the egg, and
does not extend so far towards tlie dorsal surface as in the Isopoda generally, and the
telson is bent downwards as in the Amphipoda. In Serolis the embryo is exactly similar,
and on PI. X. fig. 7 I have figured a young embryo of Serolis antarctica ; if this
figure be compared with the figures of Cymothoa in Mr. BuUar's paper, the close similarity
between the two will be at once apparent.

This fact appears to me to be very strong evidence in favour of Milne-Edwards's view
concerning the zoological position of the Serulidte, which arc regarded by him as a division
of the Cymothoadae."

Post-Emhryonie Development. — As in many other Lsopoda, the males of Serolis when
first hatched show none of the distinctive secondary sexual characters of males ; tlie time
at w^hich they assume these characters difi"ers in difi'erent species.

In Seivlis cornuta the males are at first exactly liki' the females in general aspect;
the body is more oval than in the fully-developed males, being considerably narrower
proportionately; the thoracic appendages of the third pair- are, as in the females, similar to
the succeeding thoracic limbs ; the penial filament of the second abdominal apj^endages is
short, and the sterna of the free abdominal segments resemble those of the female in being

1 Phil. Tmns., V(il. clxix. p. 505, 18T9.
- Hut. Nat. d. Crmt., 1840, t. iii.

28 THE VOYAGE OF H.M.S. CHALLENGER.

furnished with a median spine. On PI. I. are figures of a female (fig. 2), a fully
developed male (fig. 1), and a young male (fig. 3) of Serolis cormtta, which are drawn
exactly of the natural size ; and judging from the very slight difference in length between
the immature and the fully developed male, it would appear that the male does not
acquire all its secondary sexual characters until the last moult, though the comparatively
oreater breadth of the body, which also distinguishes the males of this species from the
females, is recognisable somewhat earlier.

The comparatively small number of S2:>ecimeus (seven) of Serolis necera makes it
impossible to state with any accuracy the time at which the males assume their proper
sexual characters ; the facts are as follows — of the fjur male species two are completely
adult, measuring 42 mm. in length, the remaining two are immature, the largest
measuring 25 mm. in length ; this specimen has the general appearance of a female in its
comparatively short epimera. absence of modification in the third thoracic appendage, and
in all the other secondary characters by w^hich the males of this species difi'er from the
female, with the exception of the frontal "sense organ," which resembles that found in the
adult males, and is not greatly developed as in the females ; from this it appears that
those secondary sexual characters in which the males of this in common with other
species difi'er from the female appear comparatively late, while the one sexual character
peculiar to the species is developed early.

In Serolis schythei the males reach maturity much sooner than in Serolis corniifa ;
the largest male specimen in the Challenger collection measures 30 mm. in length by
38 mm. in breadth ; the smallest male specimen, with fully developed secondary sexual
characters, is 16 mm. long by 19 mm. broad ; another male specimen, in which the
sex could only be detected by the position of the generative apertures and by the short
penial filament, measures 15 mm. in length by 17 mm. in breadth; in this species, therefore,
the secondary sexual characters which distinguish the male appear comparatively early,
and in immature males, which in other respects are outwardly like the females, the greater
proportionate breadth is recognisable ; this character is the first to appear, as also
apparently in Serolis cornuta.

Serolis hromleyana. — In this species the males difi'er from the females in the
third thoracic and second abdominal appendages, and also in the epimera, which are
shorter in the female and slope downwards at a less angle with the longitudinal axis
of the body. The young males, as in other species, are closely similar to the
females, but acquire the secondary sexual characters peculiar to the males at a
comparatively early period ; the largest male specimen of Serolis hroTiileyana measures
54 mm. in length, the smallest male, which shows all the secondary characters peculiar to
its sex, measures 25 mm. in length; the largest male specimen, which has not yet acquired
its proper secondary sexual characters, is 21 mm. in length ; another specimen 22 mm. in
length is nearly adult ; the penultimate joint of the third thoracic appendage is swollen

REPORT ON THE ISOPODA. 29

as ill the males, but the terminal claw is not yet reflected back. A single male sjjecimen
(if this species was dredged at Station 164a, which presents some interesting peculiarities
in this respect; although only 15 "5 mm. in length, it has all the secondary sexual
cliaraeters of an adult male ; the epimera are long and project outwards, the anterior
ones nearly at right angles to the longitudinal axis of the body, and the third thoracic
appendages are fully developed into prehensile organs ; the three middle joints of these
appendages, however, are not provided with the soft sensory hairs which I have noticed
in nearly all the specimens from Station 168 ; the large male specimen from Station 156
is also characterised by the same absence of sensory hairs upon this appendage, and it
appears to me to be just possiljle that the males of this species are dimorphic, one set
being characterised by the possession of tufts of sensory filaments upon the third thoracic
appendages, and the other set differing by the absence of those structures, and also by the
fact that the individuals acquire their own proper secondary characters at an earlier date.
It is also possible, of course, that this character may be a mere local variation, but in
this case its occurrence in individuals from two such widely separated localities as
Stations 164a and 156 is not a little remarkable, especially when we consider that the
depths which the species inhabit are so different (400 and 1975 ftithoms) in these two
localities.

The time at which the females of Sewlis attain to sexual maturity corresponds in
every case to that observed in the case of the males.

In Serolis cornida only the largest female examples had the ovigerous lamellas fully
developed, though rudiments of these structures are ap^Jareut in many of the smaller
individuals.

In Serolis schythei, corresponding to the early sexual development of the male, the
Challenger collection contains a female specimen only 13 mm. in length, but having
the brood lamellse fully developed and containing eggs.

Oi Serolis hromJeyana there is an adult female dredged at Station 168, only 22 mm.
in length ; in this species, as already stated, the males acquire their secondary sexual
characters at a corresponding age.

DESCRirUON OF SPECIES.

The following is a complete list of all the species of Serolis that are known to me
either from the specimens contained in the Challenger Collection or from publisheil
descriptions, with the localities and depths at which they occur, and a reference to the
first published description ; the}- are arranged in order of discover}'.

1. Serolis paradoxa (Fabr.) ( = Serolis orhignyi, il.-E.), Mantissa Insectorum ; Patagonia and the Falklaml

Islands, New Zealand (?), Senegal (?), 5 fathoms.

2. Serolis trilohitoides (Eights), Trans. Albany Inst., 1833 ; South Shetlands, Patagonia, a few fathoni.s.

3. Serolis gaudichaudii, Aud. and ]M. E., Arch. d. Mus., 1841 ; Valparaiso, a few fathoms.

4. Serolis planus,^ Dana, United States E.xpl. Exp. — Crustacea, part ii. p. 794, 1852 : Patagonia, a few-

fathoms.

5. Serolis cnneexa, Cunningham, Trans. Linn. Sue. Lond., 1871 ; Patagonia, a few fathom.*.

- 6. Serolis scJiytJiei, Ltk., Vidensk. Meddel. f. d. nat. Foren. i Kjobenhavn, 1858; Patagonia, 4-55 fathoms.

? 7. Serolis acufangida, Gr. ; Locality ?

8. Serolis tuherciilata, Cir., Archiv f. Naturgesch., 1875 ; Bass Strait.

9. Serolis latifrons CWhite), Miers, Ann. and Mag. Xat. Hist., Ser. 4, vol. xvi. ; Kerguelen, Crozets,

Acukland Islands, 1-210 fathoms.

10. Serolis sejjtemcarinafa (Miers) ( = Serolis oralis, St.), Ann. and Mag. Nat. Hist., Ser. 4, vol. xvi. ; Mai'if>n

Island, Prince Edwards Island, Kerguelen, 1-150 fathoms.

11. Serolis cornnta, Studer, Archiv f. Naturgesch., 1879; Crozets, Kerguelen, 1-120 fathcmis.

12. Serolis serrei, Lucas, Bull. Ent. Francj. ; Patagonia, a few fathoms.

13. Serolis carinata, Lockington, Proe. Calif. Acad. Nat. Sci.; San Diego, California.

14. Serolis hromleyana, Suhm, Proe. Roy. Soc. Lond., vol. xxiv. p. 591 ; off east coast of New Zealanil,

between New Zealand and Au.stralia, at lat. 37° 53' S., long. 163° 18' E. (near Antarctic Ice-
Barrier), 410, 700, 1100, and 1975 fathoms.

15. Serolis necera, F. E. P., Pro';. Zool. Soc. Lond., 1884, pt. iii. p. 331 ; oft' Eio Janeiro, 600 and 2040

fathoms.
' 16. Serolis graeilis, F. E. B., loc. eit.; off Pernambuco, 675 flithoms.

~ 17. Serolis untarcliea, F. E. B., lor. eit.; off Pernambuco, 410 fathoms; near Crozets, 1375 and 1600
fathoms.
18. Serolis australiensis, F. E. B., loe. eit.; Australia, 38 fathoms.
■■ 19. Serolis elongata, F. E. B., lor. e>f.; Australia, 30 fathoms.
"■' 20. Serolis pallirla, F. E. B., loe. eit.; Australia, 35-40 fathoms.
'21. Serolis longicaudata, F. E. P., loc. eit.; Australia, 38 fathoms.
22. Senilis minuta, F. E. B.; Australia, 38 fathoms.

From the aliove list it will be seen that the new species obtained by the Challenger are
nearly as many as those jirevionsly known. Besides the nine new species already briefly

' It seems to me legitimate to alter the termination •' ».< " into " n " as done by Grube ; I have accordingly followed
Urube in the text.

32 THE VOYAGE OF H.M.S. CHALLENGER.

noticed by myself and by Dr. v. Willemoes Suhm, there are in the Challenger collection
seven other sj^ecies which have been more or less fully described by previous writers ;
these are Serolis 2Mi'Cidoxa, Serolis schythei, Serolis convexa, SeroUs tuhercidata, Serolis
lati/rons, and Serolis septemcarinata ; some notes upon these species will be found below.

Of the. remaining six species, Serolis acutangula is probably identical ^vith some other
form, since Grube, who originally described it in 1871, omits all mention of it in his sul)-
sequently published (1875) Monograph of the genus; it is therefore useless to recapitu-
late or make any comments upon his description here. I have quoted the reference to
this description in the list of papers at the beginning of this Report. Serolis trilobi-
toides is closely allied to if not actually identical with Studer's Serolis cornuta; the
figure of this species which is given by Eights is not very good,' and the description,
which does not entirely agree with the figure, is not quite complete enough to make it
certain whether this is a good species or not.

Serolis jilana certainly comes very near to Serolis convexa, and under the description
of the latter sjiecies I have indicated the points of resemblance and difference between
the two. Serolis gaudichaudii resembles very closely both Serolis plana and Serolis
convexa, but is nevertheless an undoubtedly distinct species; the points in which it
differs from the two latter are indicated under the description of Serolis convexa. The
two remaining species, Serolis serrei and Serolis carinata, require a fuller description.

The former species is described by Lucas in the following terms : ■ — " Elle est
plus large c^ue longue, arrondi, testacee et finement tachue de points bruns. Les
six premiers segments thoraciques constituent de tres grandes lames pointues falci-
formes ponctuees, transparentes et non dentelees sur leur hordes comme chez le
Serolis trilobitoides. Le dernier segment abdominal, tricar'ene non dentele, plus large que
long arrondi et legerement sinueux dans le milieu de son bord posterieur presente une
epine assex grande, aigue, de chaque cote de ses bords latero-posterieures. La region
buccale, les pattes ainsi que tout le dessous du corps sont d'un jaune testace. Les
antennes sont testacees maculees de brun." This species, which attains a length of
27 mm. and a breadth of 36 mm., was obtained by the French vessel " Magicienne " in
the Strait of Magellan. Lucas mentions that it is closely allied to Serolis trilobitoides,
but it seems to me, from the above quoted description, that it is probably more nearly
related to Serolis schythei.

It is to be hoped that a fuller description of this species as well as of Serolis carinata
will be published. Serolis carinata, which is one of the most interesting species of the

' Studer {Archivf. Naturgesch., he. cit., p. 21, note) refers to a supposed error on the part of Eights ; the anterior
antennae are said to be represented in Eiglit's figure as if they originated below instead of above the posterior antennie.
This is not, however, the case with Eiglit's figure, but with Audouin and Milne-Edwards's copy of the figure whicli is
introduced into their Monograph of tlie genus (lot: cit., pi. ii. fig. 11) ; the absence of .shading here does make it appear
as if the anterior antenna; originated below the posterior.

^ Bull. Soc. Eat. Frang., air. 5, t. vii. p. cxlv and cxlvi.

REPORT ON THE ISOPODA. 33

genus, on account of its occurrence so far north as California, has been briefly cliar-
aeterised by Lockiugton^ as follows: — "Thorax and abdomen conspicuously keeled upon
the centre of every segment ; the first segment slightly waved on its posterior margin,
the curve of the segments increasing rapidly in such a manner that the last entirely
encloses the free abdominal segments on their sides. Caudal segment rounded at the
extremity, vnth two marginal teeth on each side at a considerable distance from the
extremity, the central carina running the entire length of the segment; last basal joint
of inner antennte longer than the flag-ellum ; flagellum of outer autenute much shorter
than either of the two of the preceding basal joints, and last basal joint about ecpial in
length to the penultimate. Eyes large, reniform, conspicuous. The texture of the
upjjer surface of a dried specimen under a two-thirds power has a somewhat squamate
appearance. Colour a greyish-brown, diversified with dots and irregular markings of
black ; hands long and slender ; dactylos ecjual in length to the manus.

" Length, 0-21 inch; width, 0-16 inch."

Two specimens from San Diego, California.

1. Scrolls paradoxa (Fabricius) (PI. V. figs. 12-14).

Oniscus paradoxus, Fabricius, Mantissa Insectoruin, Hafnife, 1787, t. i. jx 240; Systema Ento-

mologia;, Flensburgi et Lipsiaj, 1775, p. 296.
Ci/mo/hna paradoxa, Fabricius, Entomologia Systematica, Hafniw, 1792-98, SuppL, p. 301,

and t. ii. p. 503.
Serolis fabridi, Leach, Diet. d. Sci. Nat., 1818, t. xii. p. 340.

Scroll's orhiijiii/i, Audouin and Milne-Edwards, Arch. d. Mus. d' Hist. Nat., 1841, t. ii. p. 25.
Semlis orhiijniana, Jlilne-Edwards, Hist. Nat. d. Cru.st., vol. iiL p. 232.
Serolis paradoxa, Miers, Crustacea collected during Survey of H.M.S. "Alert," Proc. Zool. Soc.

Lond., 1881, p. 61.

Serolis j)aradoxa is the type species upon which the genus Serolis was founded by
Leach. The rfnimal was first ol)tained on the shores of Patagonia by Sir Joseph Banks at
the close of the last century, and these specimens were described by Fabricius as Oniscus
jxiradoxus ; in a subsequent work Fabricius altered the name to Cpnothoct, paradoxa.
In the twelfth volume of the Dictionuaire des Sciences Naturelles, Leach gave some account
of this species which he termed "Serolis fahricii." The first full description of the species
is contained in the memoir of Audouin and Milne-Edwards," and subsequently Grube^
in his important Monograph gave a fuller account of this same species, but under the
name of Serolis orhigniana. In a short note published in the Journal of the Godeffroy
Museum,* Schmeltz called attention to the identity of Serolis fahricii with another
species described by Audouin and Milne-Edwards under the name of Serolis orhigmji.
More recently Miers, in his account of the Crustacea collected during the voyage of the
" Alert," has also pointed out the identity of these two species.

1 Proc. Calif. Acad. Nat. Sci., vol. vii. p. .36. = Loc. cit, p. 25.

3 Loc. cit, p. 225. * Part -xii. p. 161.

(zool. chall. EXP. — PART xxxHi. — 1884.) Kk 5

34 THE VOYAGE OF H.M.S. CHALLENGER.

I have little doubt that both Schmeltz aud Miers are quite right in regarding these
two species as identical ; it is impossible, either from the description or the figures con-
tained in the memoir of Audouin and Milne-Edwards, to select any characters by which
the two species Serolis fahricii and Serolis orhigniana can be definitely distinguished ;
such diff'erences as there are appear to me to arise from the fact that the two " species "
are in reality merely the males and females of the same species, Serolis fahricii.

With regard to the name I have followed Miers and written Serolis paradoosa ; this
name evidently has the priority.

A number of specimens of Serolis jJctradoxa were dredged by the Challenger at the
Falkland Islands, and this, together with the adjacent shores of Patagonia, is the only
locality which the species is known with certainty to inhabit. According to Leach, Serolis
paradoxa extends to the west coast of Africa ; he makes the following remarks about its
distribution (loc. cit., p. 340) — " I have only seen two specimens ; one is in the collection
of Banks and comes from Tierra del Fuego ; the other is in my possession and was given
me by Dufresne, who tells me that he received it from Senegal." The specimen from
Senegal is now in the British Museum, and is labelled in the handwriting of Leach. The
British Museum contains another specimen of Serolis paradoxa which is labelled " New
Zealand," but I believe that in this case, as in that of Serolis schythei to be mentioned
later, the locality is not thoroughly authenticated. Miers includes Serolis paradoxa in
his list of New Zealand Crustacea apparently on the authority of this same specimen.

The males and females of this species are not distinguishable by any well marked
difference of size ; the males are, however, a little broader proportionately, as is shown by
the following measurements taken from two of the largest specimens obtained by the
Challenger.

Male, .......

Female, ......

The form of the abdominal sterna differs in the two sexes; in the male the outline is
somewhat crescentic, the posterior margin being curved and the anterior margin almost
straight ; in the female each of these segments bears a median spine upon the posterior
margin directed backwards and closely overlapping the succeeding segment. In this
character Serolis paradoxa agrees with Serolis schythei, but the spines in the females
are longer than in that species. The above measurements do not express the greatest
size to which this species attains ; there are several specimens in the British Museum
somewhat larger, and White states^ that individuals have been known to reach the
great length of 6 inches ! This last statement, however, requires confirmation.

Serolis paradoxa is, as Grube remarks,^ more nearly allied to Serolis schythei than to

1 Wiite, Description of New Species of Insects and other Annulosa, Ann. and Mag. Nat. Hist., 1843, vol. xii. p. 3GG.

2 Loc. cit., p. 225.

Length.

Breadth.

24-5 mm.

25 mm.

27-5 „

26 „

REPOET OiSr THE ISOPODA. 35

any other species, but it can easily be distiuguished by the smaller epimera and by the
shape of the caudal shield, which is more triangular than in that species ; as in Seroli.'^
schythei, the caudal shield is traversed by three longitudinal carinsB, and there is a stout
spine close to its anterior border in the middle line ; another carina runs parallel to
the anterior margin of the caudal shield, of which traces exist in Serolis schythei. The
transverse ridge of the latter is not found in Serolis paradoxa. As in Serolis schythei,
the first four free thoracic segments have their epimera separated from the terga by a
distinct suture.

The antero-lateral areas of the cephalic shield are more extensively developed in
Serolis paradoxa, so that the breadth of the anterior portion considerably exceeds that of
the posterior portion, while in Serolis schytJiei the transverse diameter of the cephalic
shield is greatest at about the level of the eyes.

Antennce. — The filament of the second pair of antennte in both the male and female
is furnished with a series of short recurved hooks ; these hooks are not found upon all the
joints of the filament, they commence to be visible (in one specimen) on the seventh,
and extend as far as the sixteenth ; in the last nine or ten of these joints there is a
continuous row on the upper surface not far from the inner margin, commencing close to
the posterior articulation and extending in a straight line up to the anterior articulation,
the row of hooks then bends inwards and follows closely the anterior edge of the
joint, terminating at its outer extremity; in the anterior joints the hooks gradually
decrease in uuml)er until in the seventh joint there is only a short row on the anterior
margin.

Similar structures are found in other species {e.g., Serolis bromleyana, Serolis gracilis,
Serolis sej^temcarinata, Serolis schythei), though in no case are the hooks so large and
conspicuous as in Serolis paradoxa.

The inner lobe of iliQ first maxilla? is nearly half the length of the outer lolie ; it con-
sists (PI. V. fig. 14) of a straight and narrow stem and an oval wider distal portion
furnished with a single spine near the lower border.

The second 'pair of maxillce has, as in all other sjDecies, two smaller anterior lobes and
a larger posterior one ; the anterior lobe is a trifle smaller than the second, and bears
at its free extremity two long spines ; the second lobe has five or six, while the largest
posterior lobe has some twenty or thirty.

The maxiUipedes are characterised by the almost square outline of the stipes, which
is quite twice the breadth of the lamina ; thedatter is clothed on the inner surface with
fine hairs; the suture which separates it from the stipes is not complete posteriorly.

The third px-dr of thoracic ap>pcndages in the male (fig. 13) are very much like those
of Serolis newra ; the second, third, and fourth joints are furnished with abundant
plumose hairs arranged in two rows, one above the other ; the upper row spring from
a stronsf ridse which runs at a short distance from the inner margin of these three

36 THE VOYAGE OF H.M.S. CHALLENGER.

joints, while the second row appears to be attached along the inner margin itself ; the
penultimate joint is swollen and pear-shaped, broader at the base than above ; along the
inner margin are some fifteen pairs of long cylindrical spines, which are of a rather
unusual form ; the distal third bears two rows of short cyhndrical branches ; the centre
of the spine appears to be hollow at the base, and the bounding membrane is continued
above into a solid axial rod, which projects for a short way beyond the anterior extremity
of the spine. This appendage and the peculiar spines upon the penultimate joint are
figured by Grube {he. cit., pL v. figs. 3, 3, a), Grube also states that the spines upon
this pair of appendages are alike in both males and females : — "Der Innenrand des 2'™
Paares Greiffiisse triigt lange an der Vorderseite gesagte Stacheln, sowohl beim Mannchen
als beim Weibchen." They are in reality quite difierent in the female ; the fourth joint
bears a row of spines arranged in pairs ; on the distal half of the joint these spines are
strong and serrated along both margins, resembling entirely the serrated spines found
upon the other thoracic limbs ; posteriorly the serrations become less marked, and the
proximal end of the joint has only smooth sword-like spines, the third and fourth joints
have none of the soft plumose hairs that are found in the males ; their place is occupied
by tufts of strong spines, some of which are serrated. In this as in all other species in
which the males have the peculiarity here described, the females are invariably different,
the third pair of thoracic appendages being in this respect closely similar to the succeeding
appendages.

The remaining thoracic appendages are not in any way remarkable. The second joint,
which is rather smaller than the first joint, is furnished with a tuft of long hairs upon the
inner surface at the distal extremity, among which are a few serrated spines ; the succeed-
ing joints, which are approximately of this arm length, the fourth being rather the longest,
have a tuft of hairs in the same position, among which are a greater number of serrated
spines ; in the penultimate joint the long delicate hairs are almost entirely absent, their
place being taken by stout spines, many of which are serrated. Along the outer margin
of the joints, with the exception of the first, are tufts of short spines, very few of which are
serrated.

The three anterior abdominal appendages, like those of Serolis scliythei, have no
plumose hairs upon the basal joint.

The suture of the operctdum is oblique.

The exopodite of the fifth pair of abdominal appendages is bifurcate.

Station 316, February 3, 1876 ; lat. 51° 32' S., long. 58° 6' W.; 4 fathoms; bottom,
mud.

REPORT OX THE ISOPODA. 37

2. Serolis convexa, Cunningham (PI. VI. figs. 9-15).

SeroKs corjvexa, Cunningham, Crustacea, &c., of H.M.S. " Xassau," Trans. Linn. Soo. Lond.,

vol xxvii. p. 498, 1871.
Serolis convexa, Studer, Isopoden gesammelt, &c., Abbandl. d. k. Akad. d. Wiss. Berlin, 1882, p. 9

(separat Abdriick).

The Challeuger obtained only a single specimen of this species, from Port William,
Falkland Islands ; I have, however, had the opportunity of comparing it with four other
specimens in the British Museum which are the types.

Prof. Cunningham's description {Joe. cif., p. 498) is as follows : — "Most nearly allied
in form to Serolis planus, Dana. Body very convex, much more so than in any other
species of the genus with which I am acquainted. A prominent carina along the mesial
line. Two last segments of pereion distinctly narrower than those which precede them.
Last segment of pleon more elongated than in Serolis planus, and possessing three well-
marked ridges — a median, interrupted in the middle, and two lateral, each terminating in
a sharp point. Eyes very prominent, and placed rather near to each other."

Two specimens were obtained by Prof. Cunningham on the north coast of Fuegia.

Prof. Studer has also published some notes upon this species in his account of the
Isopoda collected during the voyage of the " Gazelle," and he has pointed out that the
chief character by which Grube distinguished Serolis convexa from Serolis gaudichaudii,
viz., a tuft of hairs upon the antepenultimate joint of the second thoracic appendages,
is really a secondary sexual character peculiar to the males not only of Serolis convexa
but also of Serolis gaudichaudii ; before Prof. Studer's paper came into my hands I had
noted the same fact, and alluded to it briefly in my Preliminary Eeport;' the speci-
men dredged by the Challenger is a male, and it shows another character which I Ijclieve
to be peculiar to the males ; on the sterna of the last three thoracic segments is a small
patch about 2 mm. in length l.)y 1 mm. in breadth, distinguishable by its velvety appear-
ance and darker colour from the surrounding integument ; this on microscopic examina-
tion proved to be covered by a multitude of hairs exactly similar to those found upon the
second thoracic appendages, only rather shorter ; some of the segments in front also,
especially the second, have a small tuft of these hairs.

In other respects the males and females of this species do not differ greatly in appear-
ance ; the males are imperceptibly broader in proportion to their length than the females,
as shown by the foUowdng measurement taken from the male in the Challenger collection
and the single female specimen in the British JMuseum : —

Length. Breadth.

Male, ....... 2.5 mm. 20 mm.

Female, ....... 25 „ 19 „

The sterna of the ahdominal segments present no differences in the two sexes.

1 Proc. Zool. Soc. Lond., pt. iii., 1884, p. 330.

38 THE VOYAGE OF H.M.S. CHALLENGER.

The suture dividing the outer lamelhi of the opercula is accurately at right angles to
the long axis of the body in the female ; it is more oblique, slanting downwards in all the
male specimens that I have seen ; I am inclined, however, to think that this is rather an
individual variation than a mark of sex, inasmuch as nothing of the kind exists in any
other species.

Serolis convexa has been figured by Cunningham ^ and by Studer," and as both these
figures, especially the latter, show plainly the characters of the species, I hardly think it
worth while to introduce another into the present Eeport.

Serolis convexa can be easily distinguished from Serolis gaudichaudii by a number
of small characters ; the shape of the body is more oval in Serolis gaudichaudii ; in Serolis
convexa it is more pear-shaped, owing to the greater length of the caudal shield, which
terminates in a more pointed extremity ; in both species there- is a central and two lateral
carinse ; the latter are curved, and follow closely the lateral margin of the caudal shield
but at some distance from it ; in Serolis gavdic^iaudii these carinae, especially the two
lateral ones, are very faint ; in Serolis convexa the lateral carinse are strongly marked, and
terminate more or less abruptly in a short spiniform projection at the end of the middle
third of the caudal shield ; the median carina is only found in the anterior part of
the caudal shield, posteriorly it becomes obsolete ; another difference between the two
species is in the colour, and since this difference is quite constant in all the specimens
examined by me (five of Serolis convexa, four of Sei'oUs gaudichaudii) it is worth noting ;
Serolis gaudichaudii is distinguished by its dark brown colour, darker in the central
part of the body, and dotted all over with black spots of various sizes ; in Serolis convexa
the colour is of a uniform pale browm, hardly darker in the middle of the body than upon
the epimera. This description of course relates only to specimens preserved in alcohol.
Another species closel}^ allied to Serolis convexa is Dana's Serolis planco, and from a
careful comparison of the figures and descriptions given of these two species I find it
almost impossible satisfactorily to separate them. The general shape of the body, the form
of the epimera, &c., is almost identical in the two. The eyes, however, oi Serolis plana are
stated by Dana to be conical in shape, whereas those of Serolis convexa, as in all other
species, are distinctly reniform. In Serolis plana " the articulation of opercular plates is
more nearly transverse than in Serolis gaudichaudii;" there is also a lateral tooth on the
caudal shield just below termination of carina ; the median carina is obsolete posteriorly,
and the fourth segment has a low prominence just inside of the epimeral suture. The
first character is, as I have already shown, of no use in distinguishing the species ; the last
character, namely, the presence of a low prominence to the inside of the epimeral suture
of the fourth segment, is well marked in the Challenger specimen of Serolis convexa ; in
this specimen all the thoracic segments have a slight prominence, almost indistinguishable
in the anterior and posterior ones, but conspicuous in the fourth segment, where it slightly

1 Loc. cit., pi. lis. fig. 3. 2 Isopoden gesammelt, &e., loc. cit, Taf. i. figs, la, lb.

REPORT ON THE ISOPODA. 39

overlaps the succeeding segment and recalls Serolis minuta, in which species (see below
p. 77) all those prominences are highly developed and project backwards as flat conical
processes over the folloMdng segments.

The presence of a distinct lateral tooth below the termination of the carinse does
seem to distinguish Serolis plana from Serolis convexa where there is no such tooth, but
it would not be safe, I think, for the present to separate the two until a larger number of
specimens of both have been examined.

In all the three species — Serolis gaud ichaudii, Serolis convexa, and Serolis 2)lcma —
the epimera of the second, third, and fourth pairs only are separated from the terga by
a distinct suture ; in the first two species the anterior epimera are divided by a
transverse suture as in so many other species ; this suture is, however, not very well
marked, and in the specimen of Serolis convexa. obtained by the Challenger I could not
detect any trace of it, though it w^as distinctly visible in the British jMuseum specimens.

Apijendagcs. — I give here a somewhat full description of the appendages which have
not been described by Cunningham.

Antenme. — The posterior pair of antennae are decidedly longer than the anterior pair,
reaching as far as the end of the first epimera.

Of the anterior 'pair, the first joint is somewhat broad and c[uadrangular, the second
joint is narrower and a little longer ; the anterior and posterior surface of both are covered
by a few scattered hairs ; the third joint is a cylindrical rod somewhat bow-shaped, and
only slightly longer than the preceding joint ; the fourth joint is short, about one quarter
as long as the third. The filament appear to consist of about twenty-five joints, and
each joint has two sensory hairs, one situated near the anterior extremity of the joint, the
other near its posterior extremity.

The posterior pair of antennae consist as usual of five joints and a filament.

The first joint is the shortest, the second a little longer and somewhat hour-glass
shaped. The thii-d, as usual, inserted in a wedge-like fashion between the second and
the fourth ; the fourth joint is the longest of the whole appendage, is somewhat bent, and a
ridge parallel with the curved lower margin runs along its whole length ; the joint narrows
towards its extremity, where it articulates with the terminal joint, which is a little shorter
and more uniformly cylindrical in shape ; the upper margin of the two last joints is
furnished with scattered tufts of hairs. The filament has twenty-one joints, which
increase in length but diminish in thickness towards its extremity.

The mandihles have the cutting edge prolonged posteriorly into two subecjual
conical teeth ; on the upper side are two spines situated one behind the other, the
anterior one rather lonoer and broader.

The Jirst maxilhe are in no way remarkaljle.

The second maxiUce (PI. VI. fig. 14) differ from those of most other species in that the
two anterior lobes are not much smaller than the posterior, and are furnished on the outer

40 THE VOYAGE OF H.M.S. CHALLENGER.

edo-e wdtli eight or nine hairs instead of the usual two. In this respect Serolis gaudichaudii
seems to resemble .Sero/iA- convexa{cf. Audouin and Milne-Edwards, loc. cit., pi. i. fig. 11).

The onaxiUipedes (fig. 15) are of the usual shape; the lamina is furnished with a
number of long hairs upon the lower surface, and the second joint of the palp has a row
of similar hairs upon the lower surface, some way from the external margin, which, as
usual, has another row of hairs. The third joint of the palp is extremely small, and I was at
first inclined to think that this was a mere accident, and that the terminal joint of the
palp had been recently broken off, but since Milne-Edwards and Audouin figure^ the same
condition in Serolis gaudichaudii, it appears to be characteristic of these two species.

The second pair of thoracic appendages are fignved on PL VI. fig. 10; the tuft of
hairs (a) have already been noticed as peculiar to the males ; several of the spines forming
the inner surface of the pemdtimate joint are more highly magnified in fig. 11 ; the
longer spines, instead of being bifurcate, as is the rule, terminate in a gradually narrowing
extremity, the posterior margin of which is beset with a dense row of fine branches.

The third pair of thoracic appendages of the male are shown in PL VI. fig. 9-; the
terminal joint is comparatively narrow ; from the inner margin arise some eight pairs
of conical spines, the axis of which projects beyond the termination as a short filamentous
recurved process.

The remaining thoracic appendages were aU more or less damaged, with the exception
of the sixth, which is figured on PL VI. fig. 12 ; the second, third, fourth, and fifth joints
of this appendage are each furnished on the inner side with a tuft of fine pinnate hairs
like those on the second pair of appendages in the male ; on the distal border of the fourtli
joint is a row of sharp serrated spines ; the terminal claw-like joint of the appendage is
sharply bent upon itself at right angles ; in Serolis gracilis and other species those
appendages in the males are similarly modified.

In the anterior abdominal apijendages the basal joint is triangular in shape, and the
projecting (lower) angle is furnished with three plumose haii-s in the first of these
appendages, and two in the second and third as in many other species.

The opercula are traversed by a suture at right angles to the long axis.

Port William. Falkland Islands, 5 to 12 fathoms.

3. Serolis schythei, Liitken (PL II. figs. 5-13).

Serolis schythei, Liitken, Vidensk. Meddel. f. d. nat. Foren. i Kjcibenhavu, 1858, p. 98, Tab. i.

figs. 12, 13.
Serolis sdiythei, Grube, Arcliiv f. Naturgesch., 1875, p. 220, pi. v. fig. 1, pi. vi. fig. 1.

This species was originally described from a male specimen by Liitken. Grube in his
Monograph of the genus added some details to Liitken's description, and pointed out the
diflerences that exist between the males and the females.

' Tub. cit, fif's. 12, 13.

REPORT ON THE ISOPODA. 41

Tlie Challenger obtained a great number of specimens of Scroll's sclnjthvi, raugino-
from the Gulf of Peiias on the north, to the Falkland Islands on the south.

The collection of Crustacea in the British Museum contains one specimen which is
labelled "New Zealand," but I believe that it is not quite certain whether this label be
correct. With this possible excej^tion, Serolis schythei is confined to the shores of
Patagonia and the Falkland Islands.

The males of Serolis schythei differ from the females by their greater proportional and
actual breadth; the largest female specimen in the Challenger collection measures 32 mm.
in length by 32 mm. in greatest breadth, the largest male specimen measures 30 mm. in
length by 38 mm. in breadth. The greater breadth of the males is owing to the greater
length of the epimera. The sixth epimeron in this male specimen measures 17 mm. in
length, and extends for the space of about 5 mm. behind the extremity of the caudal
shield; in the female these epimera only measure 13 mm., and terminate just beyond
the end of the caudal shield. The first abdominal epimera also are longer in the male than
in the female ; the two sexes also difi'er, like many other species, in the shape of the
abdominal sterna. A third difference is to be found in the antennte, which are described
below.

The colour of Serolis schythei (in alcohol) is pale brown, becoming darker in the
middle of the body, and diversified with dark brown or black spots, which vary considerably
in their number and size in different specimens.

The cephalic shield is not unlike that of Serolis cornuta, Init the prominences and
ridges upon its surface are less developed ; there is a slight ridge dividing the antero-
lateral portions from the rest ; to the inside of and behind the eyes are two prominences
somewhat triangular in form, which correspond to those in Serolis cornuta, but are
directed more inwards ; between the two is a triangular area which forms the posterior
boundary, and owing to the comparatively sHght development of the lateral tubercles,
lies almost on the same level with them ; the disposition of these three prominences is
also like what occurs in Serolis newra, which in other respects shows considerable resem-
blances to this sj^ecies. The eyes are very large and prominent.

Tliorax. — The thoracic epimera are flat and sickle-shaped ; as in Serolis cornuta the
external half of all the epimera projects freely ; the articular processes upon the epimera
are, however, entirely absent. The first epimera are divided by a transverse ridge.
While in the majority of species only the three anterior of the free thoracic segments are
divided by a distinct suture into a tergal and an epimeral portion, in Serolis schythei there
is also a suture separating the terga and epimera of the fourth segment. The j^osterior
margin of the tergura of each segment, with the exception of the first, is curved backwards
in the middle line into a short spine ; these gi^adually tliminish in size from before liack-
wards ; the antero-posterior diameter of the first free thoracic segment is a little less
than that of the succeeding segment, which is the laro;est, and measures 3 mm. in the

(ZOOL. CHALL. EXP. — PART XXXIII. — 1884.) Kk 6

42 THE VOYAGE OF H.M.S. CHALLENGER.

female and 2 mm. in the male ; the third segment is a little smaller than the second in
the female and about the same size in the male ; the two last thoracic segments are nearly
the same size, the anterior being a trifle the larger, and measuring about one half the
diameter of the preceding segment.

On the under surface the sterna of the first two thoracic segments are, as in all other
species, divided by sutures into three portions, which resemble in every particular those
of Serolis cornuta ; the posterior thoracic segments are not so fused together as they often
are ; the sixth is quite distinct from the following ones, and is not divided into a central
piece and two wedge-shaped lateral pieces as it is in Serdlis necera and other species ; a
deep groove separates the seventh from the eighth, but it does not extend as far as the
suture which marks the boundary between the epimera and sterna.

Abdomen. — The first abdominal epimera are long, and reach beyond the end of the
caudal shield in the male, in the female they do not reach quite so far as the end of the
caudal shield ; the second epimera are short, as in Serolis necera, and only extend for a
very short distance down the lateral margin of the caudal shield ; they are not distinctly
longer in the male than in the female.

The sterna of the abdominal segments differ in the two sexes as already said ; in the
male the jjosterior margin is straight, and the two ends project backwards as short spines;
the third segment has, in addition, a short median spine ; in the female the median portion
of all three is produced into a short broad spine.

The caudal shield is hexagonal in outline ; the posterior end projects as a short spine ;
there is a distinct median keel and two lateral keels which start from the base of a strong-
blunt spine situated in the middle line at the anterior end, and terminate in two short
spines j)laced some way in front of the attachment of the uropoda; a transverse ridge,
which is prolonged backwards into three short spines, of which the median larger one is
upon the longitudinal carina, traverses the caudal shield ; viewed in profile, the caudal
shield appears to consist of two portions bounded by this transverse ridge ; the anterior
part, which possibly corresponds to the three fused terminal segments of the body, over-
laps the posterior portion or telson ; on the other hand it is possible, as suggested Ij}-
Studer, that the two obliquely running longitudinal keels mark the boundary between
the terminal segment of the body and the telson.

The two pairs of antenncB are of about the same length. The anterior pair
have a short proximal joint with fine hairs upon the upper surface ; the two succeed-
ing joints are elongated and somewhat curved ; the posterior surfece is furnished with
fine hairs ; the fourth joint is short and oval ; the filament is made up of about twenty-
three joints, of which the proximal ones are short, but gradually increase in length towards
the distal extremity. The second pair of antennae consist, as usual, of five joints and a
terminal filament ; the joints increase in length towards the distal end of the autennfe,
the last joint being the longest and considerably narrower than the rest, which are about

REPORT OX THE ISOPODA. 43

equal in diameter ; the three last joints are beset with hairs arranged in tufts or scattered
singly over the surface ; the filament is made up of from fifteen to seventeen joints,
which, like those of the anterior antennse, increase in lengtli and diminish in width
towards the free extremity ; the inner side of each joint, just before the attachment of
the joint in front, has a tuft of fine hairs ; the anterior margin of the middle joints has a
series of short curved spines like those already described in SewHs ])ciradoxa {ante, p. 35) ;
the antennae of the males possess a series of delicate lamellar processes (PL 11. fig. 6)
arranged in a single line along the inner side of most of' the joints, being absent only
from a few of the extreme distal and proximal joints ; these structures, which are very
probably sensory, take the form of oblong lamellas with rounded angles, those at the
anterior part of the joint are larger and somewhat fan shaped ; their surface is marked by
a series of grooves radiating outwards from the base of attachment.

The mandibles (PL II. figs. 12, 13) are markedly asymmetrical, as in other species.

The maxiUcB present no peculiarities.

In the maxillipedes (fig. 10) the stipes and the lamina are not separated by a
suture ; both are covered with scattered hairs, and a row of finer hairs clothes the inner
margin of the latter ; at the summit of the terminal joint of the palp is a small
protuberance carrying three stoutish hairs similar to those upon this and the preceding
joint.

T\\e first pair of amhidatory appendages are figured by Giulte in his Monograph, but
the hairs on the inner side of the penultimate joint are not quite correctly shown ; the
longer spines (PL II. fig. 7) terminate in two flat lateral expansions, and the axis of the
spine is continued into the posterior and longer of the two.

The second j^ir of amhidatory appjendages of the male (PL II. fig. 8) are modified
in the usual way {ante, p. 13).

In the remaining thoracic appendages (fig. 9) the two first joints are subequal in
length ; the third joint is about half the length of the secoml, the fiiurth slightly longer,
the fifth shorter than the fourth, and approximately of the same size as the second ; the
terminal joint is more bent and hook-like in the last pair of appendages than in any of the
others. The second joint (in the males only) has a series of about fifteen tubercles close to
the inner margin ; the third, fourth, and fifth joints are furnished with numerous long and
slender hairs as well as stouter sword-like and serrated spines arranged in tufts in the
usual way ; the last pair of appendages in the male are distinguished from the rest l)y
a greater development of hairs upon the inner surface of the terminal joints ; this is an
approximation to the marked difi'erenee that these appendages show in other species
{e.g., Serolis gracilis). In Serolis schythei, however, these hairs are not, as in the al)ove-
mentioned species, in any way different from those upon the rest of the ambulators-
limbs.

The three anterior ahdominal appendages are characterised l»y the absence of

44

THE VOYAGE OF H.M.S. CHALLENGER.

branched hairs upon the basal joint; in this they agree with Se rol is iximdoxa and the
Australian s^iecies of the genus.

The opercula have the exopodite divided by an oblique suture.

The exopodite of the gill cqypendage is bifurcate.

The uropoda are attached close to the termination of the caudal shield, and extend
a little way beyond it ; they are comparatively large and foliaceous, and furnished with
numerous branched hairs.

Station 304, December 31, 1875; lat. 46° 53' S., long. 75° 12' W. ; 45 fathoms;
bottom, green sand.

• Station 313, January 20, 1876; lat. 52° 20' S., long. 67° 39' W. ; 55 fathoms;
bottom, sand.

Station 314, January 21, 1876; lat. 51° 35' S., long. 65° 39' W. ; 70 fathoms;
bottom, sand.

Station 315, January 26, 1876; lat. 51° 40' S., long. 57° 50' W. ; 12 fathoms;
bottom, sand, gravel.

Station 316, February 3, 1876 ; lat. 51° 32' S.,long. 58° 6' ^Y. ; 4 fathoms; bottom,
mud.

4. Serolis latiffons, White (PL II. figs. 1-4).

Serolis latifrons. White, Li.st Crust. Brit. JIus., 1847, p. 106.
Serolis latifrons, Miers, E. J., Ann. and Mag. Xat. Hist., 1875, p. 74.
Serolis latifrons, Miers, E. J., Cat. New Zealand Crust., 1876, p. 117.
Serolis latifrons, Smith, BuU. U. S. Nat. Mus., 1876, vol. iii. p. 63.
Serolis latifrons, ^Miers, E. J., Phil. Trans., 1879, e.xtra vol., p. 204.
Serolis latifrons, Studer, Th., Archiv f. Naturgesch., 1879, p. 26.

This species was named and described by AVhite from specimens obtained during the
voyage of the "Erebus" and "Terror"; one of these specimens is preserved in the
British Museum, and was dredged at Eendezvous Cove, Auckland Islands. Miers first
described the species from specimens, brought home by the Transit of Venus Expedition
from Kerguelen Island, and a more detailed description of the same species is to be
found in Studer's Beitriige zur Kenntniss niederer Thiere von Kerguelensland.^

A number of specimens were dredged by the Challenger at Christmas Harbour,
Kerguelen, 25 fathoms, and two others which present some dififerences from the tj-pical
form were dredged in deeper water (210 fathoms) ofi" Possession Island.

"Without enteriirg into any systematic description of this species, which has abeady
been sufficiently done by the above mentioned authors, I may add here a few details.

Studer describes the largest specimens as attaining a length of 40 mm. and a breadth
of 30 mm. ; these are e\'idently females, which he says are 1 to 2 mm. less than the

• Archiv f. Naturgesch., he. cif., p. 2C.

EEPORT ON THE ISOPODA. 45

males. lu the Challenger collection the two largest specimens measure 32 mm. iu length
by 24 mm. in breadth, and are females with developed brood lamellae. The males are
proportionately broader than the females ; the length of the largest specimen is 28 mm.,
its breadth 24 mm. ; in one specimen only the breadth was proportionately less than in
all the rest, 28 mm. in length by 22 mm. in breadth ; the sterna of the free abdominal
segments differ but slightly in the two sexes — in the females all have a short, broad,
median spine, in the males the two posterior segments are provided with such a spine, which
is if anything rather smaller than in the female.

The colour of Serolis latifrons (in alcohol) is a dark bluish brown, becoming lighter
brown upon the epimera ; a very characteristic mark of the species is a white spot upon
the anterior part of the cephalic shield, just behind the rostrum ; the fifth pair of epimera
also are generally lighter in colour than the rest of the body.

The six posterior thoracic epimera are separated from the terga by a distinct suture
and the first abdominal segment, which in no other species of Serolis known to me has
any trace of epimera, has distinct though very minute epimera separated from the tergum
by a suture which is continuous ■ndth that dividing the epimeron and tergum of the
segment in front.

Appendages. — The second paii' of autennse are longer than the first pair ; the latter
have as usual four joints; the fourth joint is extremely short, its length being only one-
third of its breadth ; the filament has sixteen joints ; in the second pair of antennas the
terminal joint (PI. II. fig. 4) is prolonged on the ventral side into a process which extends
as far as the third joint of the filament ; the filament has twelve joints.

The mandibles are characterised by the great length of the narrow distal half, which
is about half the length of the entire appendage; the masticatory portion of the two
mandibles are shown on PI. II. figs. 2, 3; they present the usual unsymmetrical disposition
of the laminae and spines upon the lower surface.

The first pair of maxillce resemble the same appendages in other species, but the
second joint of the palp has seven or eight spines upon its extremity instead of two.

The second maxillce present no difi'erences from other species.

MaxiUipedes. — The lamina and stipes are separated by a complete suture ; the
outer margin of the stipes and cardo is clothed with fine delicate hairs ; the lamina is
furnished on its under surface with a number of long hairs which extend over the
proximal joint of the palp.

The first ambulatory limb presents no special difi"firences from that of other species.

Of the second pair in the male, the penultimate joint is rather narrow, only slightly
wider where it articulates with the preceding joint; the distal joint terminates in a
spine-like extremity which is separated by a suture; just behind the articulation of this
spine is a ridge bearing a row of fine hairs. The remaining joints of this limb are
almost smooth, and have only a few short hairs.

46 THE VOYAGE OF H.M.S. CHALLENGER.

The remaining thoracic apioendagcs, on the coiitraiy, are abundantly furnisliecl with
long, unbranched hairs, and short, stout, serrated, and smooth spines ; the latter are
■ especially developed at the distal extremity of each joint just before its articulation with
the succeeding joint.

The proximal joint of the limb is the stoutest, and except in the two penultimate
limbs, the lono'est, its margin is clothed with fine delicate unliranched hairs ; the
second joint is shorter, and the third shorter still ; the fourth and fifth joints in the
posterior limbs are considerably elongated ; the distal extremity of the terminal joint is
separated off by a suture, and ends in a sharp spine.

The abdominal appendages present no peculiarities except the terminal uropoda, which
have been well described and figured by Studer; ^ the endopodite becomes fused with the
protopodite, and is extraordinarily elongated ; the short exopodite is spine-like, and can
l)e fixed at right angles to the rest of the appendage, forming in this way a defensive
apparatus, which, as Studer suggests, no doubt secures to the animal a greater freedom
from the attacks of l)irds and other enemies. For figures and fuller description of
this structure the above-mentioned Memoir by Studer should be consulted. The
structure of the uropoda in this species recalls that characteristic of the family
Sphseromidje.

Two specimens of Serolis latifrons dredged off Possession Island in 210 fathoms
present some variations from all the other specimens ; they are both females, with fully
developed brood lamelte, and are approximately of the same size, measuring 28 mm. in
length by 23 mm. in breadth ; the proportions therefore of these specimens are nearly the
same as in the males of the typical Kerguelen form ; the sterna of the abdominal segments,
however, are quite like those in the females. In one specimen the posterior two pairs of
brood lamellse of the left side overlap those of the right, the two anterior pairs are normal.
This variety is quite different in colour, being of a uniform yellowish brown, with a few
scattered black spots, especially upon the caudal shield. The shape of the caudal shield
is different from that in the Kerguelen specimens ; it is considerably narrower, and the
lateral margins are almost straight, with only a very slight outward bulging ; the posterior
epimera of the body come therefore to project considerably beyond the margin of the
caudal shield, which is almost completely triangular in shape.

One of the specimens is figured on PL II. fig. 1, and may be compared with the
figures of Studer and Miers of the normal variety.

Station 148, January 3, 1874; lat. 46° 47' S., long. 51° 37' E. ; 210 fathoms;
bottom, hard ground, gravel, shells.

Kerguelen Island, January 13, 1874; Cascade Bay, 5-40 f.ithoms. January 17,
1874; Royal Sound, 25 fathoms.

1 Archivf. NaturgescL, 187U.

EEPOET ON THE ISOPODA. 47

5. Sei'olis sejitemcarinata, Miers (Pis., 11. fig. 14, VIII. figs. 3-5).

Serolis quadricarinafa, "White, List Crust. Brit. Mus., 1847, p. 106.
Serolis sejdemcarinafa, Miers, Ann. and Mag. Nat. Hist., 1875, p. 116.
SeroUs sepiemcarinafa,^ Miers, Phil. Trans., 1879 (extra vol.), p. 206.
SeroJig oualig, StiiJer, Arohiv f. Naturgesoh., 1879, p. 21.

That Serolis scptemcarinata is the same species as Serolis ovalis cannot be doubted ;
the descriptions and figures given l»y Miers and Studer agree in every detail.

Both these observers described the species from a single specimen only ; Studer's
description relates to a female specimen from Kerguelen, while IMiers's specimen was
dredoed at the Crozets.

The Challenger obtained this species at Kerguelen, and also off Prince Edward's
Island ; the species therefore is common to these three groups of Antarctic Islands, Intt
has not as yet been obtained elsewhere.

Studer remarks the rarity of this species as compared with Serolis latifrons, and
suggests that the absence of the spine-like uropoda found in Serolis latifrons may render
it an easier prey to its enemies ; the Challenger, however, collected a large number of
specimens of this species at Kerguelen, very nearly as many as of Serolis latifrons.

The males of this species difi'er from the females by their greater size.

The largest male specimen measures 13 mm. in length by 11 mm. in lireadth, the
largest female specimen measures 11 mm. in length by 9 mm. in breadth. All the
specimens obtained by the Challengei; with the exception of a few newly hatched young,
are almost exactly the same size as the two specimens from which the measurements are
taken, and the superiority in size of the males over the females can therefore be very
plainly seen.

The abdominal epimera are similar in both sexes.

A noticeable difference between the two sexes is to be found in the first thoracic
epimera ; the under surface of these epimera in the males is furnished with a row of
ridge-like tubercles, six or seven on either side, which are situated just external to the
attachment of the appendages ; they are a,rranged in a semicircle, with the convexity
directed forwards and outwards ; in the female there is no trace of any such structure ;
it is probable that these tubercles assist the male in maintaining a firm hold of the female
during copulation.

The general surface of the body, especially the ej^imera, is sculptured, the latter are
traversed by innumerable ridges anastomosing with each other ; on the cephalic shield
and the tergal portion of the segments the surface is covered by minute scattered pits.
All the epimera, with the exception of the first, are traversed by a crescentic ridge which

' In my opinion the catalogue name Serolis quadrimrinata ought not to have heen changed by Jliers in spite of its
being a "nomen ine2Huiii," but since the actual description of the species is under the name of Serolis septemcarinata, it
is necessary to adopt it here.

48 THE VOYAGE OF H.M.S. CHALLENGER.

follows at some distance the anterior margin of the segment ; the first epimera are not
divided by any transverse suture ; the epimera of the three succeeding segments are
separated from their terga by a suture.

The cephalic shield lias a crescentic ridge between and a little in front of the eyes
as in Serolis tubervulata (cf. PL VI. fig. 1) and other species ; its anterior margin is pro-
longed in the median line into a short rostrum, and as in other species a ridge separates
off the antero-lateral portion from the rest.

The caudal shield is trifid at its extremity, and furnished with a central carina which
runs from end to end ; on either side of this are two lateral caringe, which do not extend
along the whole length of the caudal shield, they terminate behind at some distance from
the end of the caudal shield in freely projecting spines ; the inner pair extend farther
back than the outer pair ; another carina runs parallel with the anterior margin of the
caudal shield on either side, and terminates close to the articulation of the uropoda. The
lateral margins of the caudal shield, as well as of the posterior epimera, are denticulate.
A noticeable character of this species is the prolongation of the abdominal epimera a little
way beyond the last pair of thoracic epimera ; in Serolis minuta the same thing occurs,
but in these two species only.

T\iQ first pair of antenna are a little shorter than the second pair; the filament, which
has about eighteen joints, is rather longer than the basal portion of the antenna, — the
latter is composed of four joints; the first is short, the second about twice its length, and
about equal in length to the succeeding joint, though considerably stouter than it.

In the second pair of antenncB the two distal joints of the stem are the longest, and
about equal in length to each other ; they are somewhat bow-shaped, and the anterior
margin is beset with tufts of long hairs, five to each joint in the specimen from which the
description is taken ; the filament has twelve or thirteen joints.

The mandibles show the usual asymmetry; the left mandible has a chisel-like cutting
process, the edge of which is somewhat crenate in outline ; this structure is absent from
the right mandible.

The first pair of maxillce consist as usual of a basal piece with which are articulated
two masticatory lobes ; the posterior of these is delicate and small, and l:)ears one short
spine at its expanded distal extremity as in Serolis p>aradoxa {cf PI. V. fig. 14).

The second pair of maxillai are comparatively large; the middle lobe is furnished with
four spines upon the cutting margin instead of the usual two.

In the maxillipedes the stipes and lamina are completely separated by a suture ; the
second joint of the palp is not so markedly heart-shaped as in other species.

In the second jMir of thoracic appendages the sixth joint is entire ; the fifth joint has
a row of spines upon the inner side, they are as usual of two kinds ; the longer spines
terminate in a bifid extremity, of which the anterior bifurcation is the longest ; the axis
of the spine extends between the two branches, and is rather lono-er than either.

REPORT ON THE ISOPODA. 49

One of the thinl pair cf thoracic appendages in the male is disphiyed in fig. 3 ; the
spines peculiar to this limb are confined to the projecting lower angle of the penultimate
joint ; several of these are shown more highly magnified in fig. 5.

The remaining thoracic limbs present no features of interest.

The third jyair of appendages in the male (PI. A^III. fig. 3) is rather diff'erent from
the same appendages in other species ; the penultimate joint is comparatively long and
narrow, but widens out in its posterior fourth, where six spines are attached in pairs ; at
the upper end, close to its articulation with the terminal joint, is a single pair of spines ;
the interval between this spine and the six at the hinder end of the joint is beset with a
few scattered hairs ; the posterior spines are broad and conical, and the central filament
projects a short way out from the extremity. The remaining joints of this limb are
smooth and almost devoid of spines. The other thoracic appendages (PI. VIII. fig. 4) are all
similar to each other, save that in the last pair, the third, fourth, and fifth joints are
clothed wuth a closely set row of fine delicate hairs in addition to the sharp sword-like
spines which are found here as in the other appendages ; in the female these hairs appear
to be absent. The same difi"erence between the two sexes in this appendage has been
already described in Serolis convexa {ante, p. 40), and it exists in other species. The
terminal joints of the thoracic appendages from the third pair onwards are divided by
a suture into a short distal and a long proximal half

The Jirst three abdominal appendages, like those of many other species, have the
inner angle of the basal joint prolonged into a process which bears three branched hairs
in the first and two such hairs in the two following pairs of appendages. The suture
upon the opercula is inclined at an angle with the transverse axis.

The urojMda are attached exactly halfway down the lateral margin of the caudal
shield, but do not extend as far as its extremity.

Station 145, December 27, 1873 ; lat. 46° 43' S., long. 38° 4' 30" E. ; 140 fathoms ;
bottom, volcanic sand.

Station 149b, January 17, 1874; lat. 49° 28' S., long. 70° 30' E. ; 25 fathoms;
volcanic mud ; off Marion Island, 50 fathoms.

Station 149c, January 19, 1874;. lat. 49° 32' S., long. 70° 0' E. ; GO fathoms;
bottom, volcanic mud.

Station 149D, January 20, 1874 ; lat. 49° 28' S., long. 70° 13' E. ; 28 fathdms ; bottom,
volcanic mud.

G. Serolis cor nuta, Studer (PI. I. figs. 1-lG).

Serolis corimta, Studer, Beitr. zur Kenut, &c., Arcliiv f. Xaturgesch., 1879, ]i. 19.
This species has been described by Studer in his Memoir on the Fauna of Kerguelen,'
where a figure is given of the male and certain of the appendages. The males and

I Loc. cit., pp. 21-24.
(ZOOL. CHALL. EXP. — PART XXXUI. — 1881.) Kk 7

50 THE VOYAGE OF H.M.S. CHALLENGER.

females differ from each other in their shape ; as in Serolis schythei, the male is much
broader in proportion to its length, being nearly circular in outline ; in the female
the shape of the body is oval ; this difference depends upon the greater length of the
epimera ; in the male the sixth pair extend nearly so far as the end of the terminal
spine of the caudal shield, while the two abdominal epimera extend about half way
down the caudal shield, their posterior extremities being situated on a line with the
articulation of the uropoda ; in the female the sixth thoracic epimera only just pass
beyond the articulation of the uropoda, while the abdominal epimera hardly reach as far.

The sterna of the abdominal segments differ in the two sexes ; in the male the two first
are oblong in shape, the posterior margin being slightly concave, the third is prolonged
into a fiat triangular spine ; in the female the posterior margin of all the segments is
prolonged into a blunt spine ; tlie length of these increases progressively from before
liackwards.

Studer has given a good general description of this species, comparing it with Se7'oiis
trilohitoides, to which it is most nearly allied. For the sake of completeness I give here a
recapitulation of his description, with a few additions, which applies to all the specimens
in the Challenger collection, the variations being inconspicuous and confined to the colour,
which is darker or lighter, and the number of spines upon the carina of the caudal shield,
which vary from three to six.

The length of the largest male specimen is 34 mm., its breadth 31 mm. ; the length of
the largest female specimen is 41 mm., its breadth 35'5 mm.

The length of the cephalic shield is about one-fifth of the whole length of the body ;
close to the anterior margin is a transverse ridge which runs almost parallel to it ; in
front of the eyes, and occupying the middle of the cephalic shield, is a squarish area
raised and separated off by a groove ; the posterior margin of this is slightly concave,
the two ends being somewhat produced backwards ; the lateral portions of the cephalic
shield in front of the eyes slope gradually downwards towards the side ; behind and to the
inside of the eyes is a large blunt conical tubule, one on either side ; between the two, and
forming the posterior boundary of the cephalic shield, is a flattened triangular area.

Thorax. — The epimera are broad and sickle-shaped, and the terminal portions from
the articular process outwards project freely and do not overlap each other ; the
articular processes are short, and as in many other species, there are only two to
each epimeron ; the posterior articular process of each epimeron overlaps the anterior
articular process of the succeeding epimeron.

The second, third, and fourth epimera are separated from their terga by a distinct
suture. The anterior epimera are separated into two halves by a transverse ridge, and
there is in addition an anterior ridge as in Serolis hromleyana and Serolis gracilis, which
is a continuation of the anterior ridge on the cephalic shield ; it runs at first parallel to
the anterior margin of the epimeron at some little distance from it, and then bends

EEPORT OX THE ISOPODA. 51

abruptly at riglit angles, terminating a little way in front of the second transverse ridge.
The margins of all the epimera are minutely serrated externally. The terga of the free
thoracic segments have almost the same autero-posterior diameter, the two last being
only a trifle narrower ; the sterna of the first two thoracic segments are as usual divided
by sutures into a median and two lateral sclerites ; the median sclerite of the anterior
segment is keeled, that of the second has a short keel, widening behind and extending
over its anterior half only. The posterior margin is raised into a ridge, which is continued
along the lateral sclerites, but is here rather narrower. The sterna of the three last
segments are partly fused as in other species.

Abdomen. — The caudal shield is rather more than one-third of the lencrth of the

O

whole body ; its shape is pentagonal, and the end is produced into a long spine ; there is
a distinct longitudinal keel, which is furnished with three to six short recurved spines,
the first of which is always the largest ; at the anterior end of the caudal shield are two
short spines, one on either side, and closely approximated to the middle line ; from the
outer margin of each of these runs a fold somewhat curved in its course, which terminates
a little in front of the attachment of the uropoda in a short spine ; this lateral fold is
similar to that found m. Se rolls paradoxa and Serolis schythei, and perhaps marks the
boundary of the last segment of the abdomen ; the lateral margins from the attachment
of the uropoda to the terminal spine are provided with a number of small teeth.

On PI. I. are figures of a male (fig. 1), female (fig. 2), and an immature male
specimen (fig. 3); the latter is introduced in order to show its similarity in shape to the
female (see p. 27).

The first pair of antenme are shorter than the second pair by about half their own
length ; the terminal joint of the base is large, being rather more than half as long as the
preceding joint; the filament, which is about as long as the rest of the antenna, has
twenty -five joints.

In the second pair of antennae the basal portion has as usual five joints, of which the
last is the longest, being about equal in length to both the third and fourth joints
together. The filament is nearly but not quite as long as the fifth joint, and is composed
of fifteen or sixteen joints. One of these is shown highly. magnified in PI. I. fig. 6 ;
on the inner and lower surface of some of the joints towards the middle of the filament
is a row of short lancet-shaped spines; these decrease in size towards the distal end of the
filament, and in the last three or four joints seem to be entirely absent ; they commence
to be visible on about the third joint of the filament, but are only present in small
numbers towards the distal end of the joint and close to its articulation with the one in
front. The figure (PL I. fig. G) represents the seventh joint ; these spines, which are
present upon the antennae of both sexes, are like those that are found in Serolis paradoxa,
and which have been described (ante, p. 35).

Mandibles. — The distal extremity of the right and left mandibles of a male specimen

52 THE VOYAGE OF H.M.S. CHALLENGEE.

of Serolis cornuta are shown on PI. I. figs. 7 and 8. The right mandible (fig. 7) has
upon the upper surface a broad chisel-like process which is absent from the left; the latter
is compensated by two large bifid spines instead of the single spine which springs from the
lower surface of the right mandible. In another specimen, however, these conditions were
reversed, the chisel-like plate being developed only upon the left mandible, while the
right mandible had two spines.

The Jirst pair of maxillcB are quite like those of other species.

The second pair (PI. I. fig. 9) in one specimen were asymmetrical like the mandible ;
the middle lobe of the left hand maxilla had four spines, while the right hand one (PI. I.
fig. 10) had only two; in another specimen, however, both right and left maxillae had only
two spines.

The maxilUpedes (PI. I. fig. 1 1 ) are very much covered with liairs ; the stipes, which
is separated from the lamina by a complete suture, is squarish in outline ; the palp is
broad and flat, the second joint distinctly cordate in outline.

The second ixur of anibidatory limbs in the male is modified in the usual way ; a
single spine similar to those which are found upon the inner margin of the jjenultimate
joint of these appendages is also found on the inner side and close to the distal end of
each of the two preceding joints.

The remaining ambulatory limbs are in no way remarkable ; they are more like those
of Serolis schjtliei than any other species ; the first joint is the longest and broadest ; the
second joint is narrower and slightly shorter ; it increases in "nddth towards the distal
extremity, which is furnished with a tuft of comparatively delicate spines and hairs ; the
third and fifth joints are subequal in size, while the fourth is a trifle longer ; large sword-
like spines mingled with smaller ones, and a very few serrated spines, are arranged in
tufts on the inner and outer sides of the distal extremity of these joints, and a few along
the outer margin.

The three anterior abdominal appendages of the female are displayed in figs. 12-14
of PI. I. ; as in Serolis septemcarinata and others the basal joint of the first (fig. 12)
has three bra-nched hairs like those which clothe the outer margin of the exopodite and
eudopodite of the same appendages, but smaller ; the second and third of these appendages
(figs. 13, 14) have two hairs instead of three.

The suture upon the exopodite of the fourth pair of abdominal appendages is
oblique.

The uropoda are attached aljout half way down the caudal shield, and extend as far
as its termination, the exopodite does at least, being almost half again as long as the
eudopodite ; the outer margins of both, and the distal extremity of the inner margin are
serrated and beset with branched hairs.

Station 149, January 9, 1874 ; lat. 49° 8' S., long. 70° 12' AV. ; 25 fathoms ; bottom,
volcanic mud. January 13, Betsy Cove, Kerguelen Island.

EEPOET ON THE ISOPODA.

53

Station 149b, January 17, 1874; lat. 49° 28' S., long. 70° 30' \V. ; 25 fathoms;
bottom, volcanic mud.

Station 149d, January 20, 1874; lat. 49° 28' S., long. 70° 13' W.; 28 fathoms;
bottom, volcanic mud.

Station 149E, January 21. 1874; lat. 49° 37' S., long. 70° 16' W. ; 30 fathoms;
bottom, volcanic mud.

Station 149k, January 29, 1874; lat. 48° 40' S., long. 69° 6' W.; 45 fathoms;
Ijottom, volcanic mud.

7. Serolis hromleyana, Suhm (PL IV.).

Sc.rolis hromleyana, v. Willemoes Suhm, Proo. Eoy. Soc. Lond., vol. xxiv. p. 591, 1876.
Herolis hromleyana, Challenger Briefe, No. II., Zeitsohr. f. ■\viss. Zool., Ed. xxiv. p. xix., 1874.

This species, which is cousideraltly the largest of the genus, has been already Ijriefiy
characterised by tlie late Dr. v. Willemoes Suhm from two specimens dredged in 1975
fathoms near the Antarctic ^ce-Barrier. The following description is taken from these
sjjecimens : — Length of male 54 mm., greatest breadth (at the level of the third epimera)
56 mm.; length of female 45 mm., greatest breadth 39 mm.

The male difters from the female l)y its greater size and in the greater length of the
epimera ; in both sexes the length of the thoracic epimera gradually increases up to the
sixth, which are by far the longest, and extend for a considerable distance behind the termi-
nation of the caudal shield. The extreme length of these epimera, measured fi'om their
articulation with the epimera of the preceding segment, is 47 mm. in the male and
33 mm. in the female. The epimera of the second and third abdominal segments project
beyond the caudal shield in the male ; in the female the last pair barely reach as far as
its termination. The form of the sterna of the free abdominal segments does not diflfer
at all in the two sexes.

The outline of the body is more or less oval, and the great length of the epimera,
which become extremely narrow and spiniform towards their end, serves to distinguish
this species from all others, with the exception of Serolis vecera and Serolis gracilis.
From both these species, however, it can readily be separated by numerous other points
of difference. The body is covered with scattered hairs, which are especially developed
upon the sides of, the epimera. The colour (in alcohol) is violet-grey with whitish yellow
patches upon the caudal shield and posterior portion (if the thorax ; the colour of the
living animal is described by v. Willemoes Suhm as being of " a fine lilue colour with a
red spot extending over the midst of the body and the eyes."

Cephalic Shield. — The shape of the cephalic shield can be understood by a reference
to PI. IV. fig. 1 ; it is longer than broad, owing to the projection of its lateral portions
for some way in front of the rostrum ; these antero-lateral portions of the cephalic .shield

54 THE VOYAGE OF H.M.S. CHALLENGER.

are separated from the rest by a ridge which runs from just below the rostrum to the
lateral margin on either side ; the whole cephalic shield is very distinctly separated from
the thoracic segment by a deep furrow ; the central portion which lies between the eyes
is very strongly convex, and. separable into three regions — two round convexities which lie
to the inner side of and behind each eye, and a median T-sliaped elevation, at the upper
end of which, on a level with the anterior portion of the eyes, are four tubercles arranged
in a semicircle with the concavity directed forwards ; at the hinder extremity is another
short tubercle ; the whole surface of the cephalic shield, with the exception of a flattened
area which extends from the upper end of the eyes to the transverse ridge, is covered with
minute pit-like depressions. The eyes are whitish yellow in colour.

Thorax. — The thoracic segments, like the cephalic shield, are covered with an immense
number of irregular pit-like depressions ; the posterior margin of each segment is furnished
with a minute tubercle. The epimera are of great length, and increase gradualh' from
the first up to the sixth and last pair.

The epimera of the first thoracic segment are as usual large and expanded, but narrow
rapidly towards the distal extremity, wliich is narrow and spine-like as in the succeeding
segments. The anterior margin of these epimera .bears a short forwardly directed spine at
about 3 mm. distance from the cephalic shield. The epimeron is divided into three pieces
by a Y-shaped ridge ; the two arms of the Y fomi a very obtuse angle, one is continuous
with the anterior spine already referred to, and the other passes outwards towards the
distal end ; the unpaired arm seems to correspond to the suture which is often developed
upon the first pair of epimera in other species. The two areas lying respectively in front
of and behind this median ridge are somewhat concave, while that portion which lies to
the outside of the arms is convex.

The epimera of the three succeeding segments are curved and sickle-shaped, and
project outwards at a greater angle with the longitudinal axis of the body than the rest,
which by degrees come to lie almost in the same straight line with this axis. A distinct
suture separates the dorsal portion of the three anterior free thoracic segments from these
epimera. All the epimera of the body project downwards as well as outwards, especially
in the male specimen, so that when the animal is placed upon a flat surface, the body
rests entirely upon the epimera. The second of the free thoracic segments is the widest,
and measures 4 "5 mm. in diameter ; the first and third are a trifle smaller, while the
fourth and fifth are only one-third of the diameter of the second.

The sterna of the two first thoracic segments are divided by sutures into three portions,
a median and two lateral. The median portion of the anterior segment (that which bears
the maxilhpedes) is keeled ; the sterna of the second, third, and fourth segments are
divided by a median suture into two equal halves ; the remaining segments have a rather
peculiar arrangement, which is displayed in PL IV. fig. 2 ; the middle portions of the
three segments are fused together to form a somewhat oval plate, divided by a median

■REPORT ON THE ISOPODA. 55

suture, and uj^on which two transverse furrows mark the boumlar)- l^etween the several
segments of which it is composed. The lateral portions of the sterna of the three segments
are at first fused together, but become separate just before the attachment of the append-
ages ; and a triangular plate with the apex directed posteriorly, lies between the median
and lateral portions of the sternum of the sixth segment.

Abdomen. — The first abdominal segment has as i;sual no epimera ; its width is about
double that of the preceding thoracic segment ; the second and third abdominal segments
are long and well developed, and terminate in a somewhat bifid extremity, the inner limb
of the bifurcation being considerably longer than the outer (figs. 1, 2). The sterna of the
three free abdominal segments are shown in fig. 2 ; there is a short median backwardly
projecting tubercle, longer in the second and third than in the first ; this is continuous
with a lonoitudinal rida;e which is crossed at right anoles by another ridse. The male and
female specimens, as already mentioned, show hardly any difterences in the conformation
of thefee abdominal sterna ; in the female the antero-posterior diameter is somewhat less,
and the median tubercle somewhat more pronounced than in the male.

The caudal shield, which is liroader than long, has a somewhat pentagonal contour
with rounded angles ; the uropoda are attached about half way down the side, the
posterior extremity is notched and rather turned up ; there is a median longitudinal keel,
and on either side a short flat spine near the lateral margin, and on a level with the
attachment of the uropoda ; the surface between the keel and these spines is almost flat,
but is strongly bent downwards ; the length of the caudal shield in the male is 1 7 mm. ,
almost half that of the rest of the body, its breadth 21 mm.

AjJjjendages. — The antennce are almost exactly of the same length. The first pair of .
antennse has four joints and a terminal filament made up of thirty-one joints, and equal
in length to the first four joints.

The basal joint is oval, with a truncated distal extremity; the second joint slightly
longer, with a straight outer and convex inner margin ; the third joint is half again as
long as the second and about half its width; it is cylindrical in shape; the terminal joint
is about one-third of the length of the preceding joint, and of the same shape.

The second pair of antennas have six joints and a short terminal filament ; the
sixth joint is the longest, the thml is slightly longer than the fourth; the two basal
joints ai'e small, especially the second, which only occupies one side of the antennse,
on the other (inner) side the first joint articulates directly with the third ; on the fourth,
fifth, and sixth joints are a series of ridges running transversely to their long axes,
and bearing bunches of fine hairs.

The mandibles are as usual asymmetrical ; the left hand one has a projecting chisel-
shaped process which is wanting in the right hand one.

The maxillcs are like those of other species ; the anterior pair lias nine or ten
curved spines upon the cutting edge, the most anterior of which appear to be the largest.

56 THE VOYAGE OF H.M.S. CHALLENGER.

In tlie maxillipedes (fig. 8) the stipes and lamina are not separated by a complete

suture.

The second pair of thoracic appendages in the male are modified like those of all other
species ; the inner side of the second, third, and fourth joints is clothed with fine delicate
hairs (PI. IV. fig. 6) similar to those of Sei'olis necera, l)ut more delicate and incon-
spicuous ; these structures I was only able to find in some of the specimens from Stations
168 and 169; in the large specimen from Station 15G {cf. PI. lY. fig. 5) they are cer-
tainly not present, nor in the single specimen from Station 164a. It does not appear
quite certain whether the presence or absence of these hairs is merely a local variation or
an indication of a dimorphism in the males of this species analogous to that which Fritz
Miiller' has described in a species of Tanais.

The remaining thoracic appendages are slender, like those oi Scrolls gracilis, and, as in
that species and others, the fourth joint is longer than the third or fifth joints ; the hairs
and spines are also small and delicate ; neither the serrated spines found in many species
nor the pinnate hairs found in Scrolls necera and Serolis gracilis seem to occur in this
species ; at the distal end of the penultimate joint only are there very long slender hairs,
many of which are considerably longer than the terminal joint of the appendage.

The ahdominal appenclccges are like those of Serolis antarctica.

The operculum is divided Ijy a transverse suture at right angles to its longitudinal
axis.

The uropoda are comparatively small, aud attached at the commencement of the
posterior third of the caudal shield.

Variations. — The description just given refers to two specimens dredged at Station
156 ; this species was also obtained at three other Stations, viz.. Stations 164c (400 fathoms),
168 (1100 fathoms), and 169 (700 fathoms), and some of the specimens show certain
differences, chiefly in the length of the posterior thoracic epimera and in the conformation
of the two abdominal epimera ; in one specimen (PI. IV. fig. 3) the posterior thoracic
epimera, instead of lying nearly parallel to the long axis of the body, are curved inwards
towards the extremity so as to partly enclose the caudal shield ; in this specimen the last
thoracic epimera are proportionately longer than in the type specimen, measuring 36 mm.
as against 35 mm. length of body, whereas in the type specimen these epimera, as already
stated, measure 47 mm., the length of the body being 54 mm. In the majority of speci-
mens the abdominal epimera terminate in a sharp point and are not notched at their
extremity; two other specimens, however, had abdominal epimera precisely like those figured
on PI. IV. fig. 1, and since both these specimens are small, not measuring more than half
the length of certain other specimens in which the abdominal epimera terminate simply
in a point, this character cannot be looked upon as peculiar to adults.

In all the specimens obtained at Stations 168 and 169, the ridges upon the cephalic

' Fiir Darwin (Facts for Darwin), English translation, London, 1869, p. 19 et seq.

REPORT ON THE ISOPODA. 57

shield are somewhat differeut from those figured and described in the type specimens ; a
strong ridge runs parallel to the outer margin of the epimera ; at its upper extremity it
bends backwards and passes for a short distance parallel to the boundary line of the
cephalic shield, terminating a little below the ridge which crosses the latter ; the transverse
ridge, which indicates the division of the epimeron into two parts corresponding to the
first two thoracic segments, is very slight ; the anterior spine-like process of these epimera
is not present, and the anterior margin is in consequence quite smooth (fig. 3). Many of
these specimens are more darkly coloured.

In a small specimen from Station IGtc (400 fathoms), measuring 16 mm. in length,
the outer ridge upon the anterior epimera is not present, but the abdominal epimera have
the same characters as those of the type specimens.

Station 156, February 26, 1874; lat. 62° 26' S., long. 95° 44' E. ; 1975 fathoms;
bottom. Diatom ooze.

Station 164c, June 13, 1874 ; lat. 34° 19' S., long. 151° 31' E. ; 400 fathoms ; bottom,
green mud.

Station 168, July 8, 1874 ; lat. 40° 28' S., long. 177° 43' E. ; 1100 fathoms ; bottom,
Ijlue mud.

Station 169, July 10, 1874 ; lat. 37° 34' S., long. 179° 22' E. ; 700 fathoms ; bottom,
blue mud.

8. Serolis necera, F. E. B. (PI. V. figs. 1- 11).

Serolis necera, F. E. BeJJanl, Proc. Zool. Soc. Lond., 1884, pt. iii. p. 331.

This species almost rivals Sei'oUs bromleyana in size, and resembles it in the great
length of its spiniform epimera.

The largest male measures 42 mm. in length and 48 mm. in breadth ; the largest
female measures 41 mm. in leno'th and about 40 mm. in breadth. The difference in
the proportion of length to breadth in the two sexes is caused by the greater develop-
ment of the epimera in the male ; the two sexes also differ in the characters of the sterna
of the abdominal segments and in the frontal " sense organ," which is much larger and
more evident in the female {cf. figs. 1 and 3) ; there is not such a marked difference be-
tween the lengths of the abdominal epimera in the two sexes as is often found in the
other species of Serolis.

Cephalic Shield. — The eyes are unusually large and conspicuous, 6 mm. long, bluish
black in colour owing to the comparatively small amount of pigment present; the
diameter of the cephalic shield is greater than its length ; as in Serolis hromleyana, a
transverse ridge passes from the base of the rostrum to the lateral margins of the cephalic
shield, and cuts off a small antero-lateral portion ; the anterior margin of this as well as
of the first epimera is bent upwards. Between the eyes are a number of spiniform pro-

(ZOOL. CHALL. EXP. — PART XSXUI. — 1884.) K^k 8

58 THE VOYAGE OF H.M.S CHALLENGER.

cesses which are hollow and filled up with connective tissue, two smaller median
spines and two outer ones with a bifid extremity ; the posterior margin of the cephalic
shield is indented, and forms three projections, the two outer ones being somewhat
triano-ular in shape, and tuberculated on the free margin, while the inner median one is
transversely elongated, and much like the labium in shape, with a slightly convex outer
margin.

Thorax. — Each of the thoracic segments is furnished with a median spine — the first
three are considerably longer than the rest ; the antero-posterior diameter of the thoracic
segments increases from the first to the fourth, the latter measuring 3 "5 mm. in the male;
the two last thoracic segments are comparatively longer than in Serolis hromleyana,
rather more than half as long as the preceding segment. The terga of the three anterior
free thoracic segments are separated from their epimera by a distinct suture. The epimera
of the segments gradually increase in length up to the sixth pair, which are extremely
long, measuring 37 mm. in the male, and extend backwards in a direction nearly parallel
to the long axis of the bod}^

The first epimera are larger in the male than in the female {cf. figs. 1, 3); in the latter
the margin of the epimera passes at first abruptly backwards, and then curves outwards ;
the antero-lateral portion of the cephalic shield projects outwards beyond the commence-
ment of the epimeron for a short space, and ends in a truncated slightly notched extremity;
in the male the outer margin of the first pair of epimera is quite regular. The epimera
are divided into two halves by a longitudinal ridge.

The sterna of the two anterior segments are as usual divided by sutures into three
sclerites ; the anterior segment is similar in shape to that of Serolis hromleyana ; the
median sclerite of the second segment is saddle-shaped as in the last mentioned species,
but instead of being smooth the anterior half is produced downwards into a triangular
process ; the posterior half is raised into two knobs, which are separated from each other
in the median ventral line by a suture. The three succeeding segments are divided by
a median suture which is continuous to the end of the thoracic segments. The sixth,
seventh, and eighth thoracic segments are entirely similar to those of Serolis hromleyana
above described.

Ahdomen. — The epimera of the second abdominal segment extend for a space of
about equal to half its own length beyond the caudal shield ; they are not perceptibly
longer in the male. The epimera of the third segment are very short, and only extend
to about the commencement of the lateral margin of the caudal shield ; the length of these
epimera also does not differ in the two sexes.- The posterior extremity of the first pair
of these epimera is notched as in Serolis hromleyana. The sterna of the three free
abdominal segments differ in the two sexes ; in the female the posterior margin of each
is produced into a short spine, the first being the largest and longest ; in the male the
last of the three segments only has a spine.

REPORT ON THE ISOPODA. 59

The caudal shield is almost hexagonal in outline: its lenoth in both the male and
female is about 11 mm.; it is therefore smaller in proportion than that in Serolis hromley-
ana; its breadth is about 12. mm. The uropoda are attached at about the commencement
of the posterior fourth. The median portion of the shield is slightly keeled, and bears two
spines one in front of the other, the posterior being the larger of the two. On either
side are two other short flat spines. The caudal shield of this species is very similar to
that of Serolis schythei, but it is not so distinctly carinate, and the anterior median spine
is flatter and not so large as in Sewlis schythei, while the posterior median and the
lateral spines are larger than in that species.

Appendages. — The second pair of antennae are a little longer than the flrst pair,
lu the Jirst antenme the two basal joints are of about equal length, the third
joint is twice as long as either of the preceding ones, the fourth joint short, hardly
longer than the first joint of tlie filament ; the filament is composed of about twenty
joints.

The second paiv ofantennce have the third, fourth, and fifth joints as usual covered on
the inferior surface with tufts of hairs in groups of three or four ; the filament has some
fifteen joints.

The mandibles do not appear to difi'er from those of other species.
The_^rs^ maxilke consist as usual of a stout elongated lobe and small oval lobe, both
of which articulate with the cardo ; the smaller lobe is furnished on the free cutting edge
with a single spine as it is in Serolis paradoxa {cf. PI. V. fig. 14).

The maxillipedcs are figured on PI. V. fig. 6 ; the suture between the lamina and
stipes is complete ; the palp of the mandible is abundantly furnished with setse, and the
second joint has on the inner side the small protuberance characteristic of all the deep- '
sea species of the genus (a).

The second p)air of thoracic app>endages differ from those of other species in that the
hairs which clothe the inner margin of the penultimate joint are very similar in form ;
several of these are shown on PI. Y. fig. 7 ; the longer hairs («) only difter from tlu-
shorter ones (6) by the proportions of their length and breadth.

The third pair (fig. 8) are as usual modified into a prehensile organ in the male ;
the third, fourth, and fifth joints are covered on the inner side with a dense row
of hairs which are shown magnified in fig. 9, a' ; these hairs are clothed on the
distal half with fine branches, and they closely resemble the hairs that are found on
the second thoracic appendage of the males of Serolis convexa. The fifth joint is oval,
narrowing towards the upper extremity ; it possesses the peculiar spines characteristic
of this appendage ; they are narrow and cylindrical, and terminate in a long thread
which is given ofi' from the upper surface of the spine just before its termination
(fig. 9, b'). The sixth joint is divided by a suture into a small distal portion and a long
proximal portion.

60 THE VOYAGE OF H.M.S. CHALLENGER.

The ambulatory limbs differ from those of other species in the character of the hairs ;
instead of sharp serrated spines, which are generally developed upon these appendages,
the ambulatory limbs of Serolis necera are clothed vnth. long branched hairs similar to
those found upon the three anterior abdominal appendages, but somewhat shorter. One
of the limbs of the right side is figured on PL V. fig. 10 ; the other thoracic limbs hardly
difi'er at all, except that the last is considerably shorter as in other species. On the
inner margin of the proximal joint are a number of very fine hairs, the distal half being
furnished wdth delicate branches. These hairs are exactly similar to the terminal
hair of the first antennae in this and other species, and are possibly sensory. The remain-
ing joints are provided with bunches of branched hairs, those on the inner side of the limb
being longer than those on the outer side ; the arrangement of these can be seen by an
inspection of the figure (fig. 10) ; the terminal joint forms as usual a claw which is long
and slendei-.

Abdominal Appendages. — These appendages present no peculiarities ; the basal joint
of the first pair- is furnished with three hairs upon the inner posterior angle. The two
following appendages have each two hairs in the same place.

The exopodite of the first pair of gills is divided by an oblique suture, and the
endopodite is bifid at the tip (see fig. 11).

Another specimen of this species which was dredged in 2040 fathoms (Station 318)
is in some respects difierent, but the difi'erences do not appear to me to be of sufiicient
importance to warrant its separation as a distinct species.

The epimera, instead of being long and spiniform as in aU the other specimens
contained in the Challenger collection, are comparatively short, and resemble the epimera
of the typical shallow- water forms {e.g., Serolis schythei) in being comparatively wide and
flattened; the two posterior thoracic epimera were unfortunately broken off" on both
sides of the body, but judging from what remains it seems very likely that the sixth
pair at any rate extend back beyond the termination of the caudal shield. The
anterior pair of abdominal epimera terminate a little way in front of the attachment of
the uropoda.^

Station 318, February 11, 1876; lat. 42° 32' S., long. 56° 29' W. ; 2040 fathoms;
bottom, blue mud.

Station 320, February 14, 1876; lat. 37° 17' S., long. 53° 52' W. ; 600 fathoms;
bottom, green sand.

' This specimen was mounted on a slide in glycerin ; on the same slide, entangled with the appendages of the
Serolis, were several small Nematodes, not sufficiently well preserved to exhibit any distinctive generic character. It is
of course not certain that they came from the same depth as the Crustacean, but, bearing in mind the fact that many
of the marine free-swimming Nematoidea attach themselves in a semiparasitic fashion to other animals (cf. Villot, Arch,
d. Zool. Exp., t. iv. p. 451, 1875), it is at any rate possible; so little is known respecting the distribution of the free-
swimming Nematoidea that I think it worth while to record this fact, especially as I observed other Nematoidea
among the appendages of one of the specimens of this same species from Station 320.

KEPORT ON THE ISOPODA. 61

9. SeroUs gracilis, F. E. B. (PI. III. figs. 7-18).

Seroh's ffraal/'s, F. E. Beddard, Proc. Zool. Soc. Lond., 1884, pt. iii. p. 332.

Five specimens of this species were dredged at Station 120 (675 fathoms), three males
and two females.

The males were approximately of the same size, the largest measuring 21 mm. in
length by 22 mm. in breadth; the females were much smaller, measuring 9 mm. in length,
by 8 mm. in breadth.

The chief difference between the two sexes, apart from that of size and relative
proportions of length and breadth, consists in the greater length of the epimera in the
males ; in the female specimens (PL III. fig. 8) the last thoracic epimera hardly reach as
far as the end of the caudal shield, while the first abdominal epimera only extend about
half way dowm, and the posterior abdominal epimera terminate at about the level of the
end of the anterior third of the caudal shield ; in the male (PI. III. fig. 7) the posterior
thoracic epimera are considerably longer, reaching beyond the caudal shield for a space
of about its own length ; the actual length of these epimera is 13 mm. ; the first
abdominal epimera extend a short way beyond the end of the caudal shield, and the
posterior pair to about the middle. The difference between the two sexes in the length
of the epimera is more marked in this species than iu any other known to me.

The general form of the body is circular, and the dorsal surfiice is covered with
scattered pits ; the colour (in alcohol) is a dark slate-blue, varying to reddish yellow upon
the terga of the posterior thoracic and abdominal segments.

The cephalio shield has much the same shape as in Serolis bromleyana ; the portion
lying between the eyes, which are small and inconspicuous, is strongly convex, while the
anterodateral areas are flat and depressed, and do not rise above the level of the first
thoracic epimera ; a transverse ridge running from the base of the rostrum, which is very
minute, divides the cephalic shield as in Serolis hromleijana.

Tliorax. — The first epimera are divided into three portions by two transverse ridges ;
the anterior one is continuous with the ridge that traverses the cephalic shield, it passes
at first across the epimeron and then bends backwards running parallel with the anterior
margin of the epimeron, and joins the distal end of the second ridge ; the continuation
of these two ridges passes along the margin of the epimeron closely applied to it, and
terminates some way in front of the end of the epimeron. The posterior ridge corresponds
to the line of suture between the two fused epimera of the first and second thoracic
segments.

The other epimera are flat and sickle-shaped, not spiuiform as in Scrolls hrotnlcijana
and Serolis necera; they gradually increase in length up to the sixth; the articular
processes, which unite together the succeeding epimera, are placed further than is usual
from the junction between the terga and the epimera, which gives the latter tbe appear-

62 THE VOYAGE OF H.M.S. CHALLENGER.

ance of being shorter than they really are ; the fourth and fifth as well as the three
anterior epimera are separated from the terga by a distinct suture. The antero-posterior
diameter of the three anterior free thoracic segments gradually increases from the first
to the third ; the diameter of the fourth and fifth is rather more than half that of the
third. The sterna of the two first thoracic segments are as usual divided by lines of
suture into three portions ; the median sclerite of the first segment is keeled, and that of
the second segment has a median keel which bifurcates posteriorly; the hinder half of this
sclerite is divided by a median suture continuous with that which separates the right and
left halves of the sterna of the succeeding segments. As in Serolls hromleyana and Serolis
neosra, the median portions of the sterna of the last three thoracic appendages are fused,
though the lines of division corresponding to the three segments are more strongly
marked in this species than in the two above mentioned.

Ahdomen. — The epimera of the abdominal segments have been already described
(cmtc, p. 13) ; the sterna do not appear to differ in the two sexes. The caudal shield is
squarish in outline, 7 mm. in length by 8 mm. in breadth ; its length is therefore not
(|uite one-third of that of the whole body. The uropoda are attached close to its posterior
margin. There is a slight longitudinal median keel, which is crossed at right angles by
a sinuous ridge with three convexities, one median and two lateral, which correspond
to the spines on the caudal shield of Serolis necBra and Serolis schythei ; at about the
end of the anterior third of the caudal shield is a sliort flat spine in the middle line and
two oblique ridges, one on either side of this spine ; the lateral portions of the caudal
shield are bent down.

The two pairs of anteunce. are of about equal length. In the anterior pair
the first joint is short and oval ; the second joint is a little longer, and the upper
margin projects a little way beyond the articulation of the succeeding joint, which is
nearly twice its length, narrow, and bent downwards. The filament has fourteen
joints.

The two distal joints of the basal portion in the second antenna3 are furnished with
hairs arranged in tufts along the upper margin. The filament has twelve joints.

In the maxillipedes (PI. III. fig. 10) the stipes and lamina are not separated by a
complete suture ; the second joint of the palp has a small tubercle near the base covered
with hairs as in the other deep-sea species.

The third thoracic appendages in the male resemble those of Serolis necBra in that the
inner margin of the third and fourth joints bears a number of delicate plumose hairs ;
a few are also to be found at the upper extremity of the second joint ; the penultimate
joint is swollen and considerably broader at the base ; the inner margin has about a dozen
pairs of conical papilla-like spines which grow longer and narrower towards the distal
extremity, where they come to resemble exactly the plumose hairs upon the anterior
j oints.

REPORT ON THE ISOPODA. 63

The ambulator!/ limhs are rather slender, and the joints elongated ; the fourth is always
longer than either the preceding or succeeding joint ; the spines upon these appendages
are not very much develoj^ed ; the second and third joints in all bear a few pinnate hairs
upon the inner margin close to the articulation with the succeeding joint ; the remainder
of the limb is furnished with delicate sword-like spines arranged in tufts upon the inner
side ; mixed with these are a few strong serrated spines which are most abundant upon the
distal extremity of the penultimate joint. The inner side of the third, fourth, and fifth
joints in the last ambulatory limb (PI. III. fig. 1 1) is covered with soft pinnate hairs (fig. 1 2),
like those found on the second pair of thoracic appendages of the male, and the inner side
of the first ambulatory limb is similarly provided with these hairs, though to a less extent.

The three anterior abdominal aj^pendages are like those of other species ; the basal
joint is prolonged outwards, and bears two to three branched hairs at the tip.

The suture which divides the exopodite of the opercula is o1)lique ; the cxopodite of
the gill appendage is bifurcate.

Station 120, September 9, 1873; lat. 8° 37' S., long. 34° 28' W.; 675 fathoms;
bottom, red mud.

10. Serolis antarctica, F. E. B. (PI. III. figs. 1-6).

Serolis anfardica, F. E. Bedtiard, Proc. Zool. Soc. Lond., 1884, pt. iii. p. 333.

The three species above described agree with each other and difier from all other known
species of the genus in the great development of the epimera. Serolis antarctica, the
only other deep-sea form, has comparatively short, flat epimera as in the shallow-water
species of Seivlis. This species may be distinguished by the entire absence of eyes, and
by the strongly marked sculpturing upon the dorsal surface of the Ijody.

The Challenger collection contains eight specimens besides some fragments. The
four male specimens are all fipproximately of the same length, the largest measuring
33 mm. in length by .31 mm. in greatest breadth. The remaining specimens, which are
females, vary in size; the largest measures 31 mm. in length by 26 mm. in greatest breadth.
The males, therefore, appear to be larger than the females, and also broader in proportion
to their length ; the contour of the body in the males is oval, in the females somewhat
pear-shaped {cf. PI. III. figs. 1, 3); the epimera are proportionately longer in the
males, those of the sixth pair project a little way beyond the end of the caudal shield ;
the abdominal epimera are much the same length in the two sexes, and reach about half-
way down the caudal shield ; in the female the sixth thoracic epimera do not project
beyond the caudal shield ; the second pair of abdominal epimera are a trifle longer than
the anterior pair, and Ijoth are very slightly shorter than the abdominal epimera in the
male. The sterna of the abdominal segments do not seem to difler in the two sexes.
The colour of this species (in alcohol) is violet-blue, inclining to reddish yellow in the
middle of the body. The body has a nacreous glitter when seen by oblique light.

64 THE VOYAGE OF H.M.S. CHALLENGER.

Cei)haUc Shield. — The cephalic shield is very slightly raised above the general
surface of the body ; its posterior surface is furnished with a short blunt tubercle ; a slight
ridge separates the autero-lateral portions from the rest, as in other species. The eyes
are entirely absent, their place being occupied by a small tubercle similar to the rest of
the chitinous integument, and containing no traces of any optic structures.

Tliorax. — The dorsal surface of the thorax, as well as the rest of the body, is very
much sculptured, more so than in any other species of the genus ; upon the epimera the
sculpturing takes the form of a network of ridges enclosing irregularly shaped roundish
pits ; the anterior half of the cephalic shield is sculptured in a similar fashion ; the posterior
part of the cephalic shield and the terga of the thoracic segments (especially upon their
posterior portions) are covered with thicker ridges anastomosing irregularly ; these are
most conspicuous ujion the lateral portions of the terga of the three anterior free
thoracic segments. The sculpturing ujjon the terga of the abdominal segments is very
slight. The scidpturing upon the caudal shield differed in different specimens ; in some
it resembled that of the epimera, in others the central portion between the median and
lateral carinje was occupied by a number of roundish irregularly scattered tubercles.

The posterior margin of all the thoracic as well as the abdominal segments is pro-
longed in the median line into a short blunt tubercle ; these are larger upon the two last
thoracic and the abdominal segments.

The first epimera are not divided into two portions by a suture ; the succeeding
epimera are closely applied to each other, the extreme end alone projecting freely ; they
are rather different in shape from what is customarily found in Serolis; instead of rapidly
narrowing towards the free extremit)' and terminating in a fine point, the anterior
margin runs parallel to the posterior margin of the previous epimeron until just before
the termination of the latter, when it passes abruptly backwards in a direction nearly
parallel to the long axis of the body, and joins the jiosterior margin almost at right angles.
The fifth and sixth ejiimera are more like those of other species.

The epimera of the three anterior free thoracic segments are separated from the terga
bj- a suture.

The sterna of the first two thoracic segments have the usual form (PI. III. fig. 4) ; the
median sclerite of the first segment is keeled, that of the second segment has a short keel
extending from the anterior extremity to about the end of the first third. The sterna
of the three posterior thoracic segments are similar to those of the last described species
{cf. PI. III. fig. 2) ; the male genital pores are very closely approximated in the middle
line.

One of the male specimens pi'esents an abnormality in the presence of a pair of
ovigerous lamelL^ upon the third free thoracic segment ; the lamella of the right side was
about twice as large as that upon the left side.

Abdomen. — The three anterior abdominal segments have been alreadv described ; the

EEPOET ON THE ISOPODA. 65

caudal shield mecasures 12 mm. in leugth by 12 mm. in greatest breadth in the male speci-
men, and 11 mm. in leugth by 11 mm. in breadth in the female ; it is therefore more than
one-third of the leugth of the animal ; its shape is more or less hexagonal ; the lateral
portions are strongly bent down, and the uropoda come to be attached quite on the under
surface, and are almost invisible from above ; there is a median longitudinal keel which
liifurcatesat about the end of the anterior fifth, on either side is a Y-slif>ped keel inclined
at an oblique angle ; the portion of the caudal shield which lies between the median and
lateral keels is flat, the part which lies out.-iide the inner fork of the lateral keel is bent
downwards ; the posterior end of the caudal shield is slightly bent up.

AntenncB. — In the anterior pair the two first joints are short and about equal in size ;
the third joint is narrow and long, twice tlie length of cither of the preceding joints ; the
fuurtli joint is very short ; the filament has aljout twenty-eight joints, each of which has
two sensory hairs ; the filament is nearly as long as the basal portion of the antenna.

The second pair of autennpe are longer; the filament has about twenty-one joints, and is
almost exactly equal in length to the last joint of the basal half of each of the antennje.

The mandibles are like those of other species in being asymmetrical ; the left bears on
the upper surface a chisel-like process and above a single spine ; the right has two spines.

The upper lobe of i\i(i first pair of maxillcB has ten spines upon its masticatory edge ;
the lower lobe has the usual form, an<l has Init one slender spine close to the hinder
margin of the cuttiuo; edoe.

O DO

In the maxillipedes, the stipes and lamina are completely separated l)y suture ; the
margins of both are smooth; the second joint of the palp is comparatively slender; its
inner edge is beset with hairs along the distal half; close to the middle of the joint is an
oval prominence as in the other deep-sea species.

One of the second j^ctif of ambulatory limbs in the male is shown on PI. III. fig. 5.
The distal joint is as usual bent back upon the one in front like the blade of a closed
penknife upon its handle ; the penultimate joint is considerably broader at the base, and
bears about fourteen somewhat slender spines, arranged in pairs.

The remaining ambulatory appendages (PI. III. fig. 6) are slender, and but scantily
furnished wdth slender s})ines, some of which are serrated ; these are only to be found
at the distal extremity of the third, fourth, and fifth joints, and extending for a short
way along the outer margin of the fourth and fifth joints.

The three anterior j^airs of abdominal aj)pendages have a tuft of two or three hairs
upon the projecting outer angle of the basal joint.

The suture upon the operculum is at right angles.

The uropoda are extremely small, and attached near the end of the lateral margins of
the caudal shield.

Station 122c, September 10, 1873; lat. 9' 10' S., long. 34° 4!)' W. ; 400 fathoms;
liottom, red mud.

(ZOOL. CHALL. EXP. — PART XXXUI. 1884.) Kk 9

66 THE VOYAGE OF H.M.S. CHALLENGER.

Station 146, December 29, 1873; lat. 46' 46' S., long. 45° 31' E. ; 1375 fathoms;
bottom, Globigerina ooze.

Station 147, December 30, 1873; lat. 46° 16' S., long. 48° 27' E. ; 1600 fathoms;
bottom, Diatom ooze.

The above cited Monograph of Grube contains a description and figures of a species of
Serolis (Serolis tuberculata) which diifers from all the species known at that time and
from ;dl those already described in the present Eeport by the characters of the fifth and
sixth thoracic segments ; the tergum of the fifth segment, which is generally narrower
than the preceding ones, is in this species extremely narrow, not measuring more than one-
sixth of the diameter of the segment in front, while the tergum of the sixth thoracic
segment has entirely disappeared : the Challenger obtained two specimens of this same
species, Serolis tuberculata, besides examples of four other species which agree Avith
Serolis tuberculata in the characters just mentioned ; nil these species are inhabitants of
the shallow waters off the southern and eastern coasts of Australia, and form a well-
marked group, agreeing with each other in a number of structural points. These species
I have briefly described in my " Preliminary Eeport," and named as follows : — Serolis
pallida, Serolis aiistraliensis, Serolis elongata, Serolis minuta, and Seivlis longicaudata ;
all these species, with the exception of Serolis minuta, agree witli each other and with
Serolis tubercidata in the following points, some of which are peculiar to the group,
while others again are not confined to the group, but are also to be found in other species.

They are all of small size ; the females are larger than the males (?). The thoracic
epimera are short and closely applied together for then- whole length, while the epimera
of the two abdominal segments are very short and not 2>rolonged beyond the anterior
margin of the caudal shield. The tergum of the fifth thoracic segment is extremely
narrow ; the tergum of the sixth segment is obsolete in the middle line, the suture which
separates it from the succeeding first segment of the abdomen passes forwards and
disappears underneath the segment in front {cf. PI. VI. fig. 1) in Serolis tuberculata and
Serolis 'pallida ; in Serolis australiensis, Serolis elongata, and Serolis longicaudctta the
general appearance of the two last thoracic terga is the same, but a careful inspection
shows that the posterior sutures of both segments become obsolete just before the middle
line of the body, so that which apparently is the tergum of the first abdominal segment
in reality includes also the middle part of the terga of the two last thoracic segments.
In Serolis minuta the fifth and sixth thoracic segments are not quite so narrow as in the
other Australian species. The fifth segment is divided o3' by a sutural line which is
entirely continuous from one side of the body to the other ; the sixth segment, however,
though proportionately somewhat broader, resembles that of Serolis australiensis, &c., in
being fused mesially with the succeeding abdominal segment. In the other Australian
species the rostrum is long, reaching beyond the first joint of the anterior pair of

REPORT OX THE ISOPODA. 67

aiitennre. The sterna of the abdominal segments are prolonged into stout spines in
1)oth sexes. The caudal shield is truncated at its extremity. The proximal joint of the
anterior abdominal appendages is narrow, and, as in Seivlis sckythei, the basal triangular
process furnished with branched hairs is alisent ; the suture on the operculum is at right
angles to the long axis of the 1)ody. The palp of the maxillipede has this peculiarity,
that the second joint, instead of being cordate in shape, has the two margins curved
inwards and parallel with each other.

This as3eml:)lage of characters is very distinctive of all the Australian species with the
sole exception of Serolis mimita ; this latter appears to l)e intermediate between the
other Australian species and the more typical species of Serolis such as Serolis paradoxal
in the characters of the last thoracic segments, as above stated, it more closely resembles
the former, while in other respects it comes nearer to the latter; it would be difficult to
classify it definitely with either ; for this reason, and also considering the compactness in
other respects of the genus, it appears to me inadvisable to divide Serolis into two
separate genera or sul^genera.

11. Serolis tube rcuhta, Grube (PL VI. figs. 1, 2).

Senilis tulii'iriilata, Grube, Arcliiv f. Naturgesch., 1875, p. 227.

The Challenger obtained two specimens of a small species of Serolis, which I identify
with Grube's Serolis titherculata ; one of these specimens is a male, the other a female ;
they were olitained from difi"erent localities, the male from Station 161, the female from
Station 162 ; the former specimen is unfortunately much damaged.

The female is larger than the male — it measures 19 mm. long l:)y 17 mm. broad; the
length of the male is 12 mm., its breadth about the same. It appears therefore that the
males of this species, if not smaller than the females, are broader in proportion to their
length, as is generally the case in this genus. The colour of the two specimens is rather
different ; the female is pale yellowish brown, with innumeraljle black dots ; on the
outside of each epimeron is a larger l»lack spot ; the male is of a uniform l)ut darker
brown.

I have but little to add to Grube's excellent description of this species-; in my
specimens the epimera are not so closely applied together as he describes, and this is
especially the case in the male, where the points of all the epimera project freely.
On the cephalic shield l)etween and in front of the eyes is a semicircular ridge of the
inteo-ument ; the convexity is directed forwards, and the two lateral ends are prolonged
])ackwards into two short spines; the lateral tubercles on the thoracic segments are eight
or nine in number on either side, and are situated on a low ridge which commences near
the junction of the tergal portion of the segment with its epimeral i>ortion, and terminate
a little before the middle of the segment : this ridge is longer in the thii'd free thoracic

-o

68 THE VOYAGE OF H.M.S. CHAl.LENGER.

segment than in tlie rest. The two last thoracic segments have only one tubeivle on
either side, which form the outer extremity of a slight ridge.

Anteiuice. — The first pair of antennae has a stem composed of four joints, of which
the thu'd is rather more than twice as long as either of the two basal joints ; the filament
consists of some fiftj" joints ; in the second pair of antenuai (PI. VI. fig. 2) the third
joint has its posterior border prolonged into a spine as figured byGrube;' the upper
surface of this and the succeeding joint has a strong longitudinally running ridge ; the
upper margin of the fourth and fifth joints, which are as usual the longest, is sinuous, and
a tuft of hairs springs from the summit of each of the elevations ; the filament has about
twenty joints.

In the maxillipedes the stipes is almost triangular in shape ; the lamina is pro-
portionately very stout and strong, its diameter being equal to that of the stipes. Just
below the articulation of the palp is a curved ridge ; the second joint of the palp, instead
of being heart-shaped, has its two sides almost parallel, the curvature of the outer margin
folWiuff that of the convex inner margin.

The third pair of thoracic appendages is quite, as described by Grube, but I am
inclined to think that l;)oth his specimen and mine are immature males {ante, p. 16).

The ambulatory limbs of this species are characterised by being mainly provided with
one kind of spines which are of varying length. l)ut always stout and strong. The end is
bent and seems to- be of a somewhat softer consistency than the rest. The stout serrated
spines, so characteristic of the ambulatory limbs of other species of Serolis, are only
present in small numbers in Serolis tiihercidata.

The three abdominal appendages are hardl}' diftereut from those of other species ; the
basal portion is, however, not prolonged into an angle bearing two or three plumose hairs
as in many other species ; in this respect they agree with. Serolis australiensis, &c. The
exopodite of the first pair of gills is divided into two by a transverse suture, which is at
right angles to the long axis.

Generallj^ speaking, the appendages of Serolis tuherculata are very closely similar to
those of the next species to be described.

A figure of the female is oivcn on PL VI. fio'. 1 .

Station 161, April 1, 1874; oS East Moncoeur Island, Bass Strait; depth, 38
fathoms ; bottom, sand.

Station 162, April 2, 1874; ofi" East Moncceur Island, Bass Strait; depth, 38 to 40
fathoms ; bottom, sand.

' Loc. cit., pi. V. fig. 2.

REPOET ON THE ISOPODA. 09

12. Seroh'.^ austmliensis, F. E. B. (PI. YI. figs. 3-8).

Serolii mtstralicnsi.-; F. E. Beddard, Proc. Zool. Soc. Lond., 18S4, pt. iii. p. 33-4.

Uf thi,s species three cx;imples were obtained l>y tlie Challenger oft' the coast of South
Australia, aud I have been able to compare them with a specimen in tlie British Museum
lirought from the same locality.

The largest specimen is a female (PI. VI. fig. 4) aud measures 14 mm. iu length by
1 1 mm. in greatest breadth; the two remaining specimens are both males (PI. VI. figs. 3, 7),
aud are approximately of the same size, measuring 10 '5 mm. in length and 9 mm. in
breadth.

Apart from the form of the third thoracic and second aljdominal appendages, I could
detect no marked dilierences between the two sexes, unless it be that the feiuales are
really larger than the males in this and in the other Australian species.

The general form of the body of Scrolls australiensis is oval, the male a little broader
proportionately ; the distinguishing feature of this species is the immense number of
tubercles which cover the body, and are especially large u])on the caudal shield and the
posterior margin of the segments.

The ceplialic sJi ield is broadest at the level of the eyes, where it bulges out considerably
on either side. Anteriorly and posteriorly it is narrower ; the anterior margin is prolonged
into a very long rostrum ; there is a transverse ridge which forms the anterior margin of
the caudal shield for a short distance on either side of the rostrum, and then bifurcates,
the outer branch eontinuiuQ- alono- the anterior maroin of the cei)halic shield and tiivino;
ofi' a short spine directed forwards at the level of the end of the first joint of the anterior
antennae ; the inner branch follows the margin of the cephalic shield, but at some little
distance from it, and the two unite at the lateral anterior angle, enclosing between them
a somewhat boat-shaped depression. The tubercles on the cephalic shield are arranged
in transverse rows ; there is a larger spine just to the inside of the posterior third of the
eye on either side directed backwards and slightly outwards, and a median spine about
the same size situated near the posterior margin of the cephalic shield.

Thorax. — The epimera of the first segment are not divided by a suture. The three
following epimera are closely applied to each other along their whole length ; there is a
slight break between the four anterior and the two posterior epimera ; the two latter are
closely applied to each other, but the outer margin of the fifth begins to curve backwards
a little before the outer termination of the fourth epinierou, so that the angle of the latter
projects freely. All the thoracic epimera, with the exception of the first, are separated by
a suture from the tergal portion of the segments.

The terga of the thoracic segments, as well as the epimera, are covered with minute
tubercles, which are distrilnxted in longitudinal rows running from one side of the segment
to the other ; one row, whieh is constant in all the segments, and is rather more conspi-

70 THE VOYAGE OF H.M.S. CHALLENGER.

cuous thiin tlio rest, forms tlie posterior boundary of the segment, and is continued along
the posterior maroiu of the epimera. In front of this is another row of tubercles, which
in the middle of the segment lies half way between the anterior and posterior margins ; on
either side it divides into two rows, each of which run close to the anterior and posterior
margins of the segment respectively ; in the two last thoracic segments this anterior row
of tubercles is not present. All the segments of the body, with the exception of the fifth
and sixth, the former of which, as in the other Australian species, disappears altogether in
the middle line, are furnished with a larger tubercle exactly in the median dorsal line ; these
increase in size from before backwards ; on the fifth segment (in the female specimen at
least) the median tubercle is wide, and flattened and quadrifid at its extremity.

Abdomen. — The epimera of the second and third abdominal segments extend for a
very short space beyond the lateral margins of the caudal shield ; beneath, the three
anterior segments are prolonged into a stout spine of unusual length {cf. fig. 3); the
spine of the first segment, which is the longest, completely covers the spine of the
succeeding segment ; the spines in the female appear to be a little stouter than in the
male, for in the male the spines are all rather slender; the diflferences, however, are
insignificant and not well marked.

The caudal shield is more or less triangular in outline, distinctly carinate and trun-
cated at its free extremity ; its upper surface is covered with tubercles, which have no
definite arrangement except for a median transverse row which crosses the central keel
at right angles a little below the attachment of the uropoda ; one of these tubercles on
either side, close to the lateral margin, is considerably larger than the rest.

Of the Jlrst pair of antenncB the two proximal joints are short, while the third, Avhich
is the longest, measures about twice the length of the second. The joints of the filament
are extremely short and numerous ; there are about fifty ; each joint bears two sensory
filament-s instead of the usu;J one (PI. VI. fig. 5).

In the second, pair of anteiuiCB the third joint has a large backwardly projecting
tubercle just before its articulation with the following joint as in Serolis tuberctdata ;
tliis joint is also smaller than the preceding one; the fourth and fifth joints are as usual
greatly elongated, and the outer margin is sinuous. A tuft of fine hairs springs from the
surface of each of the four elevations ; the filament consists of fifteen joints, which are
longer and more slender than the joints composing the filament of the first pair of
antennae; the upper surface of the third to the tenth joints has a row of short blunt
tubercles; one or two long fine hairs springs from the inner margin of each joint at its
anterior extremity.

Mouth Appendages. — The Hia«f//6/['s, like those of Sei-olis pcdlida. have a large and
conspicuous tooth upon tlie posterior part of the masticatory edge ; behind this is
another smaller tooth; in front the margin slopes back gradually to meet the outer
maririu of the mandible.

REPORT ON THE ISOPODA. 71

The first maxiUce are short and rather beat, and resemble those of Serolis pallida.

Thoracic Appendages. — The maxillipedes (PI. VI. fig. 6) closely resemble those of
SeroHa pallida and the other Australian species, but are not sculptured like those of the
former; the lamina terminates on the inner side in the usual way; on the outer side it is
produced into a rounded prominence, which extends some way beyond the notch on the
inner side; just behind the articulation of the palp is a broad ridge as in Serolis pallida ;
the anterior mai'gin of the stipes is crenate; the second joint of the palp is not so distinctly
cordate in shape as in many species, and resembles in this particular the other allied
Australian forms.

The thoracic appendages are furnished with two kinds of spines — (1) short broad
serrated spines like those of Serolis schythei and many other species, (2) longer and more
delicate spines, which are somewhat thicker on the outer edge than on the inner; the
extremities are bent inwards; these spines seem only to Ije found on the appendages of
the Australian species. The proximal joint of all the ambulatory limbs has a number of
fine branched hairs on the inner surface like those of Serolis necBva and other species; the
second joint is a little shorter, and has one long hair on the inner side just before its
articulation with the succeeding joint; the third, fourth, and fifth joints are short, but
increase in length up to the fifth. One of the thoracic appendages is shown in fig. 8 ; the
others are similar except that the three penultimate joints increase in length in tlie
posterior limbs; in the appendage figured it wdll be seen that the spines on the outer
side arise from step-like processes, on the three penultimate joints the numl:)er of these
steps gradually increases in the posterior appendages. In the male the second thoracic
appendage, as in all other species, is modified into a prehensile organ ; the penultimate
joint is rather more elongated than usual, and its two sides are almost parallel ; on
the inner surface I counted in one specimen nine of the hairs peculiar to this joint.

The first three pairs of abdominal appendages have no hairs upon the basal joint,
and the two sides of this joint are nearly parallel ow^ng to the absence of the inner
projecting angle.

Station 162, April 2, 1874: Lit. :VJ' 10' 30" S., long. 146' 37' E.; 38 fathoms;
bottom, sand and shells.

13. Serolis elongata,F. E. B.

Serolis eloiifi'da, F. E. BeJJarJ, Proc. Zaal Soc. Loiiil., 1884, pt. iii. p. 335.

Although I have been able to examine only a single female example of this species,
its characters appear to me to be sufliciently diflerent to retain it as a distinct species.

The specimen is a female with fully developed ovigerous lamellse ; its greatest length is
10 mm., its greatest breadth 6'5 mm. It is most nearly allied to Serolis aiistraliensis.
from which, however, it differs m several respects.

72 THE VOYAGE OF H.M.S. CHALLENGER.

From the tiljove measurements, when comparecl with tliose of SeroUs australiensix
(ante, j). 68), it wOl appear that SeroUs elongata is rather narrower, the length being
proportionately greater than the breadth.

The main difference, however, between tlu- two species is the development of
tubercles upon the dorsal surface of the body ; SeroUs austraUensis is to be distinguished
from all other species of the genus by the immense number of tubercles upon the
segments of the body, and also upon the caudal shield ; in SeroUs elongata the dorsal
surface of the body is by comparison almost smooth ; this cannot be owing to the
difference of age ; the female specimen of SeroUs elongata, although actually smaller
than SeroUs austraUensis, is perfectly mature, with fully-developed ovigerous lamellfe ; and
as no other species that I have been alile to examine undergoes any change, except mere
increase in size, as soon as it has attained to maturity, there is no reason to suppose that
Sei'oUs elongata is peculiar in that respect. As in SeroUs austraUensis, each of the
segments of the body is furnished with a curved hook -like spine in the middle line ; a
row of short tubercles occupies the hinder portion of each of the segments, and is
prolonged on to the epimera ; besides these there appear to be a few scattered
tubercles over the rest of the segments and the epimera, which are very inconspicaous,
and contrast with the strongly tulierculated surface of the body in SeroUs austraUensis.

The caudal shield has the same general shape that it has in the last mentioned species,
with serrated margins and a longitudinal carina. There is also a lateral carina on either
side bearing a short spine, which is situated about half way down the caudal shield, and a
little below the place where the uropoda are attached, and terminating at the end of the
l)ody by becoming fused with the central caiina ; as in SeroUs austraUensis, these lateral
carinse are serrated. Between these and the central carina is a short ridge running
obliquely towards the margin of the caudal shield from a point a little below and to one
side of the commencement of the central carina ; the general surface of the caudal shield
is smooth, and there are only present a few scattered tubercles, especially developed in
the neighbourhood of the two lateral carinas.

Port Jackson, Sydney, 30 fathoms.

14. SeroUs longicaudata, F. E. B. (PL VII. figs. 8-10 ; PI. VIII. figs. 1, 2).
SeroUs longicaudafu, Y. E. Beddard, Proc. Zool. Soc. Lond., 1884, pt. iii. p. 336.

Of this species the Challenger obtained one immature female ; its length is 7 nun.,
its breadth 5 mm.

The general form of the body is peculiar, and unlike that of th(> typical members of
the genus; the anterior portion of the body, comprising the head, thorax, and free abdominal
segments is almost completely circular, and the caudal shield jirojects backwards for a
considerable distance, being proportionately longer than in any other of the species

EEPOET OX THE ISOPODA. 73

known to me, while the epimera are all short and abruptly truncated, reaching in no case
beyond the lateral margins of the caudal shield.

The cephalic shield terminates in front in a comparatively long rostrum ; liehiud, the
suture which separates it from the thoracic segment is incomplete in the middle line, and
for a space on either side of it extending to nearly as far as the level of the eyes ; the
cephalic shield as well as the rest of the body is quite smooth, and free from tubercles.

Tliora.e. — The epimera of the first thoracic segment are entire and devoid of any trace
of a transverse suture ; the epimera of the remaining thoracic appendages are \evj short,
and have the appearance of being truncated at their free extremity; the anterior mai-gin
of the epimeron, instead of passing insensibly into the outer lateral margins, meets it almost
at right angles, and the outer margins run liackwards in a direction almost parallel to the
long axis of tlie body ; the epimera of the three anterior free thoracic segments are
separated by a distinct suture from their terga. The epimera are extremely short, as may
be seen in PI. VIII. figs. 1, 2, where this species is figured. The two last thoracic
segments have the same characters that are peculiar to the other Australian species
of the genus ; the tergum of the fifth is extremely narrow, not more than one-fourth
the breadth of the segment in front ; the tergum of the sixth segment is entirelv absent.
The sutures which separate both segments from the succeeding and preceding ones
entirely disappear close to the middle line of the body.

The outer margins of all the thoracic epimera are faintly serrated. Veutrally the middle
portion of the segments is elevated into a broad ridge which becomes higher towards the
middle line, and slopes off gradually in the direction of the epimera ; in the sixth
segment this ridge is still more marked, and lieing develojied upon its posterior border
overlaps the terminal thoracic segment. The terminal segment of the thorax bears on
either side, close to and just above the attachment of the first abdominal limb, a circular
aperture which may l)e the outlet of some gland. I observed a similar pair of orifices
in Serolis i'>cdlida, and in several other species.

Abdomen. — The epimera of the second and third alidominal segments extend as for
as the edge of the caudal shield ; the outer margin of the second is concave, that of the
third nearly straight. The ventral portion of the first three segments is furnished with
a central triangular keel which projects some way back as a stout conical spine ; the
spine is largest upon the first segment, and its cavity communicates with the exterior by
several large fenestras upon the lower surface (PI. VII. fig. 8).

The caudal shield has a somewhat pentagonal outline, and terminates in an abrujitly
truncated extremity; the dorsal surface has a middle and two lateral carina); the portion
which lies beyond the latter is strongly bent down ; the posterolateral margins ai'e
slightly denticulate.

Appendages. — The anteniue are displayed in figs. 9 and 10 of PL VII. The anterior
pair (fig. 9) are rather shorter than the second pair ; their terminal filament has thii'teen

(ZOOL. CUALL. EXP. — PART XXXHI. — 1884.) I'^k 10

74 THE VOYAGE OF H.M.S. CHALLENGEE.

joints. In the posterior antennse (fig. 10) the filament has ten joints ; the two last
joints of the basal portion of the antenna are furnished with tufts of fine hairs springing
from shallow depressions on the anterior surface.

The ambulatory limbs are remarkable in that they are only furnished with com-
paratively slender, soft, bluntly terminating spines; no serrated spines appear to be
present. The inner side of the first joint of all these appendages has a row of about a
dozen fine branched hairs entirely like those found in many other species ; the second
joint in. all is rather smaller than the first, and has on the inner side just before its
termination a single long slender spine ; the remaining joints are subequal in size and
comparatively short ; the fourth and fifth joints in the penultimate pair of appendages
are longer and narro^\^er than in the preceding limb, and about half as long again as the
third joint.

The last pair of thoracic appendages is as usual small.

The three first abdominal a])pendac)es have the basal portion comparatively long
and narrow, and as in other Australian species the inner and lower margins are not
prolonged into a triangular process furnished with two or three branched hairs.

l!.\x& fourth pair or opercida have the exopodite divided by a suture at right angles to
the longitudinal axis, and terminating exactly at the level of the attachment of the
uropoda ; the latter are attached at about the middle of the caudal shield, and extend
exactly as far as its termination; the endopodite is slightly shorter, and at the same time
slightly broader than the exopodite ; the margins of both are smooth, and only slightly
crenate at the distal end ; they bear no branched hairs.

Station 161, April 1, 1874; lat. 38° 22' 30" S., long. 144° 3G' 30" V/. ; 33 fathoms;
bottom, sand.

15. Serolis pallida, F. E. B.(Pls. VII. fig. 1 ; VIII. figs. 6-16).

Senilis jKillida, F. E. Bed Jar J, Proc. Zool. Soc. Lond., 1881, jit. iii. p. 335.

Of this species two specimens were obtained, a male and a female. The female is the
larger, measuring 16 mm. in length and 13 mm. in breadth; the male measures 9 mm.
in length and 7 mm. in breadth.

The body is oval, somewhat pear-shaped, and recalls Serolis convcxa ; as in that
species the epimera are closely applied to eacli other, and only in the last three thoracic
epimera are the extremities freely projecting. The colour (in alcohol) is a uniform pale
brown, with t\A'o darker patches on each side of the third free thoracic segment, the
anterior portion of the caudal shield is whitish grey. The surface of the body is quite
smooth and free from tubercles except for a series, one to each segment, occupying the
median line.

REPORT ON THE ISOPODA. 75

The cephalic shield is almost triangular iu shape, from the great development of the
ocular promiuences aud a large median backwardly projecting spine ; the rostrum is lono-
and slender, and reaches nearly as far as the distal end of the second joint of the posterior
antennas ; the anterior margin of the cephalic shield is thickened into a ridge, which
bifurcates at the edge, the two branches being directed forwards and enclosing a deep
cup-like space ; shortly before the Infurcation a small spine-like process is given off
anterioi'ly.

Thorax. — The epimera are short, gradually increasing iu length up to the sixth pair;
the first epimera are entire as in the other Australian species, and not divided by any
transverse suture ; at the upper extremity is a short ridge on either side, which extends
for about one-sixth of its length parallel to the anterior margin of the epimerou.

In the three succeeding epimera the curvature of the outer margin is very slight,
which gives them the appearance of being abruptly truncated, The fifth epimera are more
sickle-shaped, since the outer is inclined at a smaller angle to the posterior margin ; the
outer margin of the sixth epimera is concave.

The terga of the thoracic segments, •nith the exception of the first and the two last,
have a median hooked spine directed upwards and Ijackwards ; these increase slightly in
size from before backwards ; the antero-posterior diameter of three anterior free thoracic
segments is about the same ; the fourth is not more than one-fifth as wide as the
preceding segments, and the tergal portion of the last thoracic, as in other Australian
species, has entirely disappeared.

Abdomen. — The epimera of the second and third abdominal segments only reach as
far as the margin of the caudal shield ; they are ec|ual in length. The terga of the three
segments are furnished with a spine like that in the thoracic segments ; these spines,
which are rather smaller than those on the thorax, increase in size from before backwards.
The sterna of these segments are produced into a long median spine, which is larger in
the first segment than in the two succeedinc!' ones.

The caudal shield in the female measures 5 "5 mm. in length, and is therefore rather
more than one-third of the length of the entire animal ; it is irregularly hexagonal in
outline, and keeled ; the extremity is notched ; the uropoda are attached about half way
down ; just below and to the inside of the spine-like process which covers the articulation
of the uropoda is a minute flattened spine on either side.

The two pairs oi antennce are approximately of the same length. The l^asal j(jint of
the first pair (PL VIII. figs. 7, 8) has three strong tubercles on its upper surface ; the
second joint has a stout tubercle on the posterior margin projecting backwards ; the
filament has twenty-four joints, each of which is furnished with two sensory hairs (fig. 8),
as in Serolis austral iensis.

In the second pair of antennre (PI. YIII. fig. 6) the fifth joint is very nuu'li enlarged ;
it is not quite so long as the preceding joint, but wider ; the filament is short, being

76 THE VOYAGE OF H.jr.S. CHALLENGER.

composed of nine joints. Tlie second and third joints of the antenure are raised into
tubercles on the upper surface.

Mouth Appendages.— T\x& mandibles (PI. VIII. figs. 9, 10) as well as the maxillipedes
(fig. 12) are much sculptured, the under surfiice being raised into a number of ridges
separated by deep depressions as shown in the figure ; the masticatory edge, instead of
being comparatively straight and smooth, as in the majority of .species, is denticulate, one
tooth on its posterior boundary being specially prominent. On the upper surface (fig.
10) are two spine-like processes.

The moxillce do not difi"er much from those of other species; the anterior pair
(fig. 11) have a short l)asal joint, and the terminal joint is much bent.

The maxiUipedes are shown on fig. 12 of PI. VIII. ; the under surface of the basal
portion, instead of being flat and smooth, as is ordinarily the case in Serolis, is traversed
by a number of ridges, the direction and form of which are displayed in the figure ; the
second joint of the palp has the peculiar shape that it has in Serolis austmliensis. The
outer margins, instead of being convex, are concave and almost parallel with the inner
margins ; they are traversed from end to end hy a ridge, close to and cpxite parallel with
the outer margins.

The second pair of thoracic appendages are shown on fig. 13 of PI. VIII., and
several of the spines from the inner surface of the penultimate joint on figs. 14, 15 of the
same plate. The latter are very characteristic in shape — the longer spines terminate in
two large oval expansions traversed by longitudinal striae which converge at the proximal
extremity ; the anterior of the two is shorter and broader than the posterior ; but at the
hinder end of the joint they become much smaller and nearly equal in size and similar
in shape ; between the two wing-like processes the axis of the spine is continued into a
thicker cylindrical tapering extremity which reaches a trifle beyond the level of the
posterior wing-like process.

The third pair are in the male modified in the ordinary way (PI. VIII. fig. 16).
The penultimate joint is oval, and furnished on the inner surface with six or seven pairs
of cylindrical spines, the axis of which is prolonged into a short filiform process. The
first joint, as in the succeeding ambulatory limit, has a row of fine branched hairs on the
inner side.

The remaiyiing thoracic appendages are stout and strong, and furnished with serrated
spines, especially upon the outer surface ; the second joint has invariably a single slender
spine .springing from al)0ut the middle of the inner surface; the tliird, fourth, and fifth
joints increase progressively in size, the fifth joint Iteing nearly or quite as long as the
second, though narrower.

The tliree first ahdominal appendages have no inner angle bearing hairs upon the
basal joint.

The suture which traverses the exopodite of the operculum is at right angles

REPORT OX THE I80P0DA. 77

to the longitudiual axis, and at tlie level of the end of the first joint of the
uropoda.

The xiropoda are attached just l>efore the end of the anterior half of the caudal shield;
the exopodites are longer and reach very nearly up t(i the distal extremitv of the caudal
shield ; they are oval in shape, and terminate in a blunt extremity ; the outer margin is
serrated nearly as far as the articulation ; the eudopoditc is relatively broader, and ends
in a truncated notched extremity, the outer and the posterior margins are serrated ; no
hairs were found upon these appendages, but it is very prol)able that they may have
become detached.

Station 162, April 2, 1874; lat. 39' 10' 30" S., long. 146° 37' R; 38 fathoms;
bottom, sand and shells.

Station 163, June 3, 1874; off Port Jackson; 30 to 35 fathoms.

16. Serolls minuta, F. E. P.. (PI. YII. figs. 2-6).

Seroh's miimfa, F. E. Beddard, Proc. Zool. Soc. Lond., 1884, pt. iii. p. 3.37.

The Challenger collection contains only one specimen of this species, which is a male ,
and measures 5 mm. in length and 5 mm. in diameter ; this species, therefore, if
full grown, is the smallest known.

In general shape Serolis minuta resembles very closely Serolls cornuta; the outline
of the body is almost circular, and the caudal shield projects only a little way beyond the
circle. A conspicuous keel runs down the middle of the body.

The cephalic shield terminates in front in a short and stout rostrum; the anterior
portion, as iu most other species, is traversed l)y a ridge [cf. PI. VII. fig. 2) arising fi-om
the base of the rostrum ; the ridge is continued on to the epimera ; the posterior margin
is provided with three blunt tubercles, of which the middle one is the largest ; each of
the following segments is similarly produced into a Ijluut tubercle at the median point
of the posterior margin.

Thorax. — Thej^>'.s'; thoracic segment is entire, and not separated into two portions by
a transverse line of division as is the case in so many other species. The dorsal surfoee
of the remaining segments is prolonged on either side into a triangular process which
slightly overlaps the succeeding segment ; these processes, which are hollow, serve for the
attachment of the muscles moving the limbs ; they are situated on the tergal portion of
the segment close to its junction with the epimeral portion ; while those of the tliird,
fourth, and sixth segments are the largest and most conspicuous.

The tergal portion of the second, thinl, and fourth segments is separated by a distinct
suture from the epimera. The sixth segment is partially fused with the first abdominal
seo-ment, the suture which divides them being incomplete for a short space on either
side of the median line ; its epimera extend about as far as the first third of the caudal

78 THE VOYAGE OF H.M.S. CHALLENGEE.

shield; the outer margins of the epimera in all the segments are smooth, without
serrations or hairs. On either side of the male generative pores is a slit-like orifice as
in Serolis pallida, &c.

Abdomen. — The second and third segments are provided with epimera which extend
farther than the epimera of the sixtli thoracic ; those of the third segment reach nearly
as far as the middle of the caudal shield. The ventral portion of the three anterior
abdominal segments is shown on PL VII. fig. 2', together with the appendages belonging
to them ; they are oblong in shape, and each overlaps the succeeding one ; the posterior
margin of the first is almost straight, in the others slightly convex.

The ccmdcd shield is almost triangular in shape, and ends in a blunt prolongation ;
the upper surface slopes gently downward on cither side from the central keel ; the
Interal margins commencing from the attachment of the terminal appendages curve
inwards and then slightly outwards, becoming almost parallel just before their termination.

Antennce. — One of the antennae of the first pair is figured on PL VII. fig. 4 ; it
consists as usual of four joints and a terminal filament ; the proximal joint is round and
entirely free from hairs ; the second joint is the largest, its lower surface is furnished wdth
a row of short hairs which are continued on to the succeeding joint ; the third joint is
smaller than the second, and the fourth is still smaller. The filament is made
up of ten joints, of which the first eight are subequal ; the penultimate joint is very
small, and the last slender and elongated. The second pair of antennae (PL VII. fig. 5)
are about one-third longer than the anterior pair ; the basal portion consists of five joints,
of which the last is the longest ; the three last joints are fiarnished with bundles of hairs
arranged irregularly over the lower surface. The filament is made up of ten joints, and
is almost exactly of the same length as the filament of the anterior antennae, which is an
unusual circumstance.

The mcmdihles present the usual form, and terminate in a Ijluut masticatory edge.

Thoracic Appendages. — The large prehensile organs which form the second pair of
thoracic appendages are in general form entirely similar to those of other species, but the
spines developed upon the inner margin are as usual distinctive ; several of these are
shown in PL VII. fig. 7.

The third pair are modified into a prehensile organ which presents some peculiarities
distinguishing it from the same apjjendage in other species of Serolis. Fig. 3 represents
the last three joints of the right hand appendage viewed in profile and from beneath.

The terminal joint is furnished with a remarkable tongue-shaped process arising from
the inner side close to the distal end ; alone; this runs a median crest like the midrib of
a leaf. The penultimate joint has five pairs of conical bent spines which are almost
exactly similar in shape to those of Serolis convexa. The fourth joint has a bundle of
fine closely-set long hairs on its inner surface, as is the case in Serolis neaira ; the third
joint has several smaller bundles of precisely similar hairs separated by intervals from each

REPORT ON THE ISOPOPA. 79

other ; this recalls the same appendage in Serolis necera, where, liowever, the third joint
is completely covered on its inner side with a dense bundle of hairs.

The succeeding thoracic appendages differ from the same appendages in all other
species of Serolh, by the fact that they are provided only with long slender hairs ; the
serrated spines so generally found on the ambulatory limbs are entirely absent. The
first ambulatory limb of the left side (fourth thoracic appendage) is displayed on PI. VII.
fig. 6. As in other species, the proximal joint is the largest and has no hairs ; the second
joint has a few hairs on the inner surface ; the three following joints are furnished with
hairs arranged in laindles as shown in the figure, and more abundant^ developed upon
the outer than upon the inner edge.

The remaining ambulatory limbs increase slightly in size with the exception of the
last, which, as in other species, is the smallest of the series. In the structure and the
arrangement of the hairs upon the several joints, they present only a few very slight
differences from the one figured ; for example, the second joint bears a single long hair
upon its outer surface, except in the last pair, where there are three, separated from each
other Ijy eijual intervals.

The first three abdominal appendages present no special characters worthy of remark,
except that the basal joints are entirely unprovided with hairs, and i^eseml)]e therefore
Serolis schythei.

The terminal pair of abdominal appendages — the uroj^oda — are attached close to
the upper end of the caudal shield ; both the distal joints are narrow and elongated,
and slightly serrated upon the outer margin ; the inner joint is the shorter of the
two, and its posterior margin is markedly dentate, and bears a number of hairs.

The colour of this species (in spirit) is brown, owing to the very slight development
of pigment, which is chiefly concentrated along the lateral portions of the terga and the
marginal portion of the caudal shield.

The specimen was dredged at Station 161, off the entrance to Port Philip, Australia.
on April 1, 1874, in 38 fathoms.

80 THE VOYAGE OF H.M.S. CHALLENGER.

GEOGRAPHICAL AND BATHYMETRICAL DISTRIBUTION.

The geographical range of the genus Serolis is almost entirely restricted to the
southern hemisphere ; so far as is known at present, this is the case with the abyssal
as well as the shallow-water species ; there is only one exception in Serolis carinata, a
species which has been described by Lockington/ and said to occur so far north as at Sau
Diego in California.

The shallow-water species of Serolis, with the excej^tion of Serolis carinata and a
more doubtful exception, Serolis j^aradoxa,^ are confined to the Antarctic area.

Within this area there appear to be four centres of distribution, corresponding in fact
to all the land masses that lie wdthin it — (l) the shores of South America as f;ir north as
lat. 30°, the Falkland Islands and the South Shetlands ; (2) Kerguelen, the Crozets,
and Marion Island ; (3) New Zealand (?) ; (4) the shores of Southern and Eastern Australia.

A Kerguelen species, Serolis latifrons, is also known to occur at the Auckland
Islands, off the south of New Zealand, a single specimen having been obtained at
Rendezvous Cove in that island during the voyage of the " Erebus " and " Terror." It
seems very probable also that the genus will eventually be found to inhabit the shores of
New Zealand, though at present there is no certain evidence to that effect. Miers, in his
list of New Zealand Crustacea, includes Serolis paradoxa, apparently on the authority
of a specimen in the British Museum, and the same collection of Crustacea contains a
sino-le example of a species which I have identified with the Patagonian Serolis schytliei,
and which is labelled " New Zealand" ; in both these cases, however, I believe that the
locality is not authenticated beyond a doubt. Considering the general similarity between
the Crustacean fauna of the whole " Antarctic region " from Patagonia to New Zealand,
it seems very probable that Serolis is an inhabitant of the shores of New Zealand. I have
called attention later (p. 82) to the fact that Serolis hromleyana occurs off the shores of
New Zealand in deep water.

From the shores of South America seven species have been described ; these arc
Serolis paradoxa, Serolis trilohitoides, Serolis gaudichaudii, Serolis plana, Serolis schythei,
Serolis convexa, and Serolis serrei ; of these species Serolis gaudichaudii extends farther
north than any of the rest; the original specimen was obtained by M. Gaudichaud''
near Valparaiso. Cunningham* also mentions that he obtained it at the same locality.
Serolis schythei was cbedged during the voyage of the Challenger as far north as the
Gulf of Peiias on the west coast ; it also occurs in the Strait of Magellan and at the

1 Loc. (dt.

2 ThLs species is stated by Dr. Leacli, on the authority of Dufresne, to inhabit tlie shores of "Western Africa,
about the river Senegal, but it has never subsequently been obtained from that locality.

^ Audouin and Milne-Edwards, Arch. d. Mm. dHist. Nat., loc. cit., p. 25.
* Loc. cit.

EEPOET OX THE ISOPODA. 81

Falkland Islands. Serolis trilohitoides is said by Eights to inhabit the coasts of the
South Shetland Islands, as well as the neighbourhood of Cape Horn; the remaining species
seem to be restricted to the Strait of Magellan and the extreme south of Patagonia.

It is possible that Serolis trilohitoides will eventually prove to be the same species
as Serolis cornuta from Kei-guelen ; the two are at least very closely allied.

With this exception the species that inhabit Kerguelen are in every case quite
different from the South American species. Besides Serolis cornuta, two others inhabit
the shores of Kerguelen, viz., Serolis Jatifrons and Serolis sei)temcarinata ; the first of
these occurs also in comparatively deep water (210 fathoms) off the Crozets. Serolis
septemcarinata is common to all three groujis of Antarctic Islands, Prince Edward and
Marion Islands, the Crozets, and Kerguelen, — while Serolis cornuta was dredged off the
Crozets durinoj the cruise of the " Gazelle."

Finally the shores of the southern and eastern parts of Austraha are inhabited by
six species o£ Serolis, viz., Serolis tubercidata, Serolis australiensis, Serolis longicaudata,
Serolis elongata, Serolis minuta, and Serolis pallida; these species, with the exception of
Serolis minuta, form, as has already been pointed out {ante, pp. 65, 66), a well marked sub-
division of the genus, differing more from either the Kerguelen or the South American
species than any of these do from each other.

It is rather premature to draw any general conclusions from these facts, even with
regard to the distribution of the genus Serolis alone ; but it may at any rate be pointed
out that the distribution of this genus, as at present known, seems to necessitate the
division of the southern hemisphere into two distributional provinces, (l) an Antarctic,
reaching from South America to New Zealand, and (2) an Australian.

The genus Serolis seems to attain to its greatest development in point of number of
individuals on the shores of Patagonia and at Kerguelen; v. Willemoes Suhm states Hhat at
Kerguelen Serolis forms no less than 20 per cent, of the Crustacean fauna ; and that " a
large species (Serolis cornuta) is the predominant and most characteristic form of all the
Crustacea in the shallow water of the Antarctic Islands."

It is true that ' nearly as many species are now kuowTi from Australia as from
Patagonia, but the genus does not appear to form an important element in the fauna of
the first mentioned locality ; only a very few specimens, not more than two or three, of
any of the six species were obtained by the Challenger ; the fact that no sjiecies have
been pre'^dously described" either by resident naturalists or from collections made by
exploring vessels, also indicates the rarity of the genus in this region. In Patagonia, on
the other hand, there are not only a comparatively large number of species, but the
number of individuals is also great, though apparently not forming so important an
element in the fauna as at Kerguelen.

1 Proc. Roy. Soc, vol. sxiv. p. 590.

- With the sole exception of one specimen of Serolis tubercuhta described by Grube, as quoted above.

(ZOOL. CHALL. EXP. — FAKT XXXHI. — 1884.) Kk 11

82 THE VOYAGE OF H.M.S. CHALLENGER.

The deep-sea species of Serolis have a wider range to tlie north than the shallow-water
species, though as j^et none have been obtained north of the equator; since there are only
four deep-sea species known, and, ■n^ith the exception of Serolis bromleyana, only a small
number of specimens of each were dredged, it is perhaps rather premature to draw any
deductions from the facts, and the following notes must be accepted for what they are
worth.

In the first place, it must be noted that in no case cio any of the shallow- water species
pass the 300 fathom limit ; nor are any of the deep-sea species known to inhabit shallow
water ; the shallow- water are specifically distinct from the deep-sea forms. I may correct
here a misleading statement in Gerstaecker's account of the Isopoda in Bronn's
Thierreiohs, from which it would appear that one species is common to " deep " and
•'shallow" water; on p. 241 of the above quoted work, Gerstaecker gives a list of the
itmge in depth of the family SeroUdte, and one species, which is my Serolis antarctica, is
stated to occur in 100 f:\thoms off the Bitiziliaji coast, and again in 1375 and 1600 fathoms
in the neighbourhood of the Crozets; 100 is a mispriut for 400, which is the actual depth
at which the species was dredged.

Two out of the four deep-sea species have a comparatively wide horizontal as well as
vei'tictil distribution ; one of these, Serolis antarctic<t, occurred at Station 120 (675
fathoms), off Peruambuco, and again at Stations 146 and 147 (1375 and 1600 fathoms),
between Prince Edward Islands and the Crozets ; the other, Sei-olis bromleyana, was
obtained at four localities between Australia and Xew Zealand, Station 164b (410
fathoms), at Stations 16S and 169, off the east coast of New Zealand, in 1100 and 700
fathoms, and again, considerably to the south, close to the Antarctic Ice-Barrier, at Station
156 (1975 fathoms) ; Gei"staecker, in the work already alluded to, calls attention to an
obvious corollary from these farts (which have been alreadv mentioned in v. TVillemoes
Suhm's Preliminary Keport on the Crustacea observed during the voyage of the
Challenger'), namely, that these two sj»ecies, as well as others which have a wide
distribution, are found in deeper water passing southwards from the equator to the pole ;
the facts in the distribution of Sc7-olis hwmleyana appear to me to furnish grounds for
another deduction, that the size of the individuals increases as they pass southwards and
into deeper water; the specimens dredged at Stations 164b and 169 (410 and 700 fathoms
re-spec tively) are all small; out of the nine or ten specimens dredged at Station 168,
farther south and deeper water (1100 fathoms), five are of considerable size, almost twice
as large as those obtained at the two first-mentioned stations; finally, at Station 156, the
southernmost point at which the species was dredged, two specimens half again as large
as the largest of those from Station 168 were dredged up froni 1975 fathoms.

St'jWi.!!! antarctica also agrees in these respects with Serolis hromleyana. though the
facts in this ease are not so strong, inasmuch as only a single specimen was dredged at

' Ptoc. Spy. Soc. LokA., voL xsIt. p. 5S5, 1S76.

REPORT ON THE ISOPODA. 83

the northernmost station in comparatively shallow water (Station 120, 675 fathoms); this
specimen is, however, distinctly smaller than any of those obtained in deeper water at
Stations 146 and 147.

It must be remembered, of course, that Gerstaecker's statements as well as mine
depend after all upon very few facts; it would lie extremely rash at present to insist
upon any such generalisation as has been put forward by Gerstaecker in the work already
quoted, but it. seems worth while to call the attention of naturalists to the focts such as
they are.

The remaining deep-sea species were dredged close to the east coast of South America;
Serolis gmcilis from a single Station (Station 120), off Peruambuco, in 675 fathoms, and
Serolis neara from two Stations close together and a little farther to the south, off Buenos
Ayres, at Stations 320 and 318, in 600 and 2040 fathoms respectively; 2040 fathoms is
the greatest depth which the genus is kno'uii to inhabit.

It appears therefore that the deep-sea forms of the genus, although not absolutely
confined to the neighbourhood of the great continents, attain to their greatest development
both in number of species and individuals in this situation, and are never found at any
distance from some land — continent or oceanic island.

The genus Serolis has evidently originated in the southern hemisphere, probably
r6und the shores of the south polar continent, and has thence s^^read northwards, its
range being apparently limited by temperature ; accordingly we find that in every case
those species which occur near the equator (Serolis gracilis, Serolis antarctica, Serolis
necera) occur there in deep water where the conditions, as far as temperature is concerned,
are not so different from the conditions which must obtain on the shores of Kerguelen and
Patagonia ; the one fact, however, which seems to militate against such an hypothesis is the
occurrence of Serolis carinata in shallow water as far north as San Dieg;o in California. It
must be remembered, however, that the temperature of that portion of the Pacific is not so
high as might be expected from its latitude ; a cold current from the Antarctic area sweeps
along the western shores of South America, and the existence of this current has perhaps
rendered it possible for Serolis carinata (or its ancestors) to migrate farther to the north
than would be possible, for example, on the eastern shores of the same continent ; more-
over, a glance at the map of the world will show that here alone is there any dii'ect
land communication between the area occupied by the shallow-water sj^ecies of the genus
Serolis in the southern hemisphere and the more northern regions ; elsewhere tracts of
deep water have possibly aided in preventing tbeir access to the equatorial regions and
the northern hemisphere, though it seems more probable, from what has abeady been
said, that the distribution of the group has been more restrained by conditions of tem-
perature than by any other cause.

Comparing the deep-sea with the shallow-water species of Serolis, it appears ( 1 ) that
the genus is pre-eminently a shallow-water genus, the number of deep-sea forms being

84 THE VOYAGE OF H.M.S. CHAIiLENGER.

comparatively small ; (2) that, as has already been poiuted out, the deep-sea are in all
cases distinct from the shallow-water species ; (3) that the deep-sea species show certain
peculiarities, notably in the structure of the eyes, which, as has already been described
(p. 20 et seq.), are either entirely absent (Serolis antarctica) or, if present, show great
evidence of functional degeneration ; none of the deep-sea species possess well-developed
eyes. To compensate for the want of eyes, there is a great development of sensory hairs
on certain of the appendages ; the males of Serolis necera, Serolis hromleyana, and Serolis
gracilis have, upon the third, fourth, and fifth joints of the third thoracic appendages,
tufts of sensory hairs, which have already been described (pp. 55, 59, 62 ; PI. IV. fig. 6 ;
PI. V. fig. 8). This structural feature is not, however, peculiar to the deep-sea species,
inasmuch as it is also found in Serolis paradoxa ; l)ut since it occurs in three out of the
four, and Serolis 'paradoxa is the only shallow-water species in which I have noticed it,
it may be considered as characteristic. Serolis antarctica does not agree with the other
deep-sea species in this respect, but the first pair of antennae are furnished with a larger
number of sensory filaments than is usual — two upon each joint of the filament ; several
shallow-water species, however, Serolis pallida, e.g., and Serolis convexa, present the same
character.

In two of the deep-sea species, Serolis hromleyana and Serolis neaira, the genus
attains to its greatest size, and these are indeed among the largest of the Isopoda ;
as a general rule the deep-sea representatives of the Isopoda are not distinguishable
from their shallow-water allies by their greater size ; there are exceptions to this rule,
notably in the case of Bathynomus, a deep-sea genus recently described by Milne-Edwards,
which is no less than 9 inches long; and the Challenger collection contains a specimen of
another Isopod belonging to the same family Cymothoadse, which is also of considerable size.
The elongated and spine-like epimera of Serolis necera and Serolis hromleyana, and also,
though to a less extent, of Serolis gracilis, are unlike anything that is met with in the
representatives of the genus from shallow water, where the epimera are always moderately
developed in comparison. In all the deep-sea species, without exception, the ambulatory
limbs are furnished with comparatively few spines, which are generally soft and delicate.
The strong sword-like and serrated spines so commonly found in the shallow-water
members of the group are either completely or partially absent ; a very general character,
inasmuch as it is found in two out of the four deep-sea species (Serolis newra and
Seivlis gracilis), is the presence, upon the ambulatory limbs, of plumose hairs similar to
those which are found upon the abdominal appendages ; 'in Serolis . nemu especially are
these plumose haii's developed in great abundance. They have been more particularly
described above, on pp. 55, 5G.

The maxillipedes in all the deep-sea species possess a short tubercle on the inner
side of the middle joint of the palp, which may represent some kind of sense organ,
though the hairs with which it is thickly covered are in no way different from the hairs

REPORT ON THE ISOPODA. So

which cover the rest of the palp. This is represented in PL III. tig. 10, a, which is drawn
from the maxillipede of the right side of Serolis gracilis ; with this figure may be com-
pared PI. I. fig. n, which represents the same appendage in Serolis cormita; this
character is so trifling, that if it were not reguhirly present in all the deep-sea species,
and as regularly absent from all tlie shallow- water species, with which I am acquainted,
it would indeed be hardly worth mentioning. In a young specimen of Serolis antarcticn
from the brood cavity of the mother, in which the appendages are still in a comparatively
undeveloped condition without any hairs and s})ines, this jnominence is conspicuous upon
the palp of the maxillipede, and is armed upon its ujiper surface with a short pointed
spine ; it is possibl)* the rudiment of some structure highly developed in the ancestors
of the group.

NOTE.

In the Plates which ac(-om]>aLiy this Report the figures of the animals themselves
were in most cases drawn Ijy Mr. Mintern from the actual specimens ; the appendages
were lithographed by him from my drawings. When not otherwise stated the figures are
magnified from 10 to 30 diameters.

(ZOOU OHALI. EXP. PART XXXIII. 1884.)

Kk

PLATE I.

(ZOOL. CHALL. EXP. PART XXXIIL— 1884 )—Kk.

PLATE T.

Serolls cornuta.

\

Fie. 1- -Jale, natural size.

Fig. 2. Female, uatural size.

Fig. 3. Immature male, natural size.

Fig. 4. Terminal joints of one of the anterior antenna3 to show the sensory hairs (6).

Fig. 5. Terminal joints of one of the posterior antennoe.

Fig. 6. Isolated joint towards the middle of the flagellum of posterior antenna.

Fig. 7. Distal half of left mandible, upper surface.

Fig. 8. Distal half of right mandiljle, upper surface.

Fig. 9. Maxilla of second pair of appendages.

Fig. 10. Same appendage of opposite side to show the occasional asymmetr}' of the
maxilljB.

Fig. 11. Maxillipede.

Fig. 12. First abdominal a].)pendage of right side.

Fig. 13. Second abdominal appendage of right side.

Fig. 14. Third abdominal appendage of right side.

Fig. 15. Several of the hairs fringing the endopodite and exopodite of abdominal
appendages.

Fig. IG. A jiortion of one of the same ; more highly magnified.

The Voyage of H.M.S'' Challenger"

Is op o da PI -I;

i__-^yll I I'U

Mint-ci'ti Bros .litK.

SEROLIS CORNUTA. Studer

PLATE 11.

PLATE ir.

Figs. 1-4. Serolis latifrons.

Fig. 1. Seroli'fi latifrons (variety), female.

Figs. 2, 3. Terminal portions of mandibles, upper surface.

Fig. 4. Terminal joint of second antennn, with commencement of ilagellum.

Figs. 5-13. Serolis schythei.
Fig. 5. A single joint from the filament of anterior antenna ; h, sensory hair.
Fig. 6. Three joints from filament of posterior antenna in male.

Fig. 7. Spines from the inner surface of penultimate joint of second thoracic appendage.
Fig. 8. Third thoracic appendage of male.
Fig. 9. One of the ambulatory limbs.
Fig. 10. Masillipede.
Fig. 1 1 . Upper lip.

Figs. 12, 13. Distal end of mandibles, upper surface.
Fig. 14. Serolis septemcarinata, nerve cords and ganglia.

The Vcvd-ge of H-M,S "Challenger"

Isopoda.PLII.

Miraerr, Bros Uth.

I-4.SER0LIS LATlFROflS.WKite 5-l3.SEROLiS SCH YTH El , Luiken

SEROLIS SEPTEMCARINATA,Miers

PLATE III.

(ZOOL. CHALL. BXP. — PART XXXIII. — 18S4.) — Kk.

PLATE III.

Figs. 1-6. Serolis Antarctica.

Fis. 1. Male, dorsal surface.

Fig. 2. Male, ventral surface.

Fig. 3. Female, dorsal surface.

Fio-. 4. Sclerites aud appendages in region of mouth, prepared by boiling in caustic
potash.

Fig. 5. Third thoracic appendage of male.

Fig. 6. One of the ambulatory limbs.

Figs. 7-13. Serolis gracilis.

Fig. 7. Male, dorsal surface.

Fis. 8. Female, dorsal surface.

Fig. 9. Mandible, lower surface.

Fig. 10. Maxillipede, lower surface.

Fig. 1 1 . One of last pair of thoracic appendages of male.

Fig. 12. One of the hairs which fringe inner surface of distal joints of same appendage ;
more highly magnified.

Fig. 13. One of the second pair of antennae.

The Voyage of H M. ^'.'Challenger'

Isopocia , PI. III.

l-e SEROLIS ANTARCTlCA.Beddard 7-12 . SEROLIS GRACI LIS, Beddard.

Mintern Bros htK

PLATE IV.

PLATE IV.

Serolis bromleyana.

Fig. ]. Male, dorsal surface.

Fig. 2. Male, ventral surface.

Fig. 3. Male (variety), with longer epimera.

Fig. 4. Female, dorsal surface.

Fig. 5. Distal joints of third thoraci('. appendage of male.

Fig. 6. Distal joints of another individual fringed with numerous sensory hairs (a).

Fig. 7. Second maxilla.

Fig. 8. Maxillipede.

The Voyage of H.M S'."C"hiaJlenger'

Isopoda . PI . IV.

SEROLIS BROIVILEYANA,Suhm.

Mintern. Bros . litK

PLATE V.

(ZOOL. CUALL. EXP. — p^unxxiui.— 1SS4.)— Ivk,

PLATE V.

FiofS. 1-11. SeKOLLS NE.ERA.

D

Fig. 1. Male, dorsal surface.

Fig. 2. Male, ventral surface.

Fig. 3. Female, dorsal surface.

Fig. 4. Female, ventral surface, displaying the eggs witliin the lirood cavity.

Fig. 5. Tip of the filament of anterior antenna to show the presence of two kinds of
sensory hairs (it, h).

Fig. G. Maxillipede.

Fig. 7. Spines fringing inner surface of penultimate joint of second pair of thoracic
appendages.

Fig. 8. One of the third pair of thoracic appendages of male.

Fig. 9. Hairs from penultimate joint of same appendage.

Fig. 10. A portion of one of the ambulatory limbs.

Fig. 11. One of fourth pair of alxlominal appendages.

Figs. 12-14. Serolis paradoxa.
Fig. 12. Distal lialf of one of the third thoracic appendages in female.
Fig. 13. Distal half of one of the third thoracic appendages in male.
Fig. 14. One of the first pair of maxilljs.

Ke Voyage of H.M. S. ChallenCer'!

Isopoda Pl.V.

I— II SER0LI5 NE/ERA.BeddarA,

Mxrxtern- Bros . litK,

12-14. SERO LIS PARADOXAFatncius.

PLATE VI.

PLATE VI.

Figs. 1-2. Serolis tubercdlata.

Fie. 1. Female ; maonified three diameters.
Fig. 2. One of the second paii' of auteuuai.

Figs. 3-8. Serolis australiensis.

Fig. 3. Male, ventral surface ; magnified three diameters.

Fig. 4. Female, dorsal surface ; magnified three diameters.

Fig. 5. Two joints from filament of first antenna ; h, sensory hairs.

Fig. 6. Maxillipede of left side.

Fig. 7. Male, dorsal surface.

Fig. 8. One of the thoracic limbs.

Figs. 9-15. Serolis convexa.
Fig. 9. Second thoracic appendage of male ; a, tuft of sensory hairs.

Fig. 10. Third thoracic appendage of male.

Fig. 11. Two hairs from inner side of penultimate joint of second thoracic appendage

Fig. 12. Terminal thoracic appendage of male.

Fig. 13. One of the hairs fringing the distal joints of the same appendage.

Fig. 1 4. One of the second pair of maxillae.

Fig. 15. Maxillipede of right side.

TKe Voyage of H.M. S!' Challenger'!

Isopoda . PI -VI.

Mintei-n. Bros lit-h -

I-2.SER0LIS TUBERCULATA, Grate. 3-8.SER0LIS AUSTRALI ENSIS .Beddard.

9-15. SEROLIS CDNVEXA, Cunningham,

PLATE VIL

(ZOOL, CHALL. KXP. — PART XXXIII. --1884.) — Kk.

PLATE VII.

Fig. 1. Serolis 2icdlida, iemale ; magnified two diameters.

Figs. 2-7. Serolis minuta.

Fio-. 2. Male : maQ;uified about uiue diameters.

Fig. 2'. Abdominal sterna and appendages ; b, penial filament.

Fig. 3. Third thoracic appendage of male, right side.

Fig. 4. Antenna of first pair.

Fig. 5. Antenna of second pair.

Fig. 6. One of the ambulatory limbs.

Fig. 7. Spines fringing the penultimate joint of the second thoracic appendage.

Figs. 8-10. Serolis longicaudata.
Fie:. 8. Sterna of last thoracic and three first abdominal segments.
Fig. 9. Antenna of first pair.
Fig. 10. Antenna of second pair.

The Voyage of H M .5"CKallenger''

Isopoda Pl.VII

MirAer:\ Btq^ 1;1.K

SEROLIS PALLIDA.Beddard. 2^-~ SEROLIS M i N U TA , Beddard

8-10. SEROLIS LONGI CAUDATA.Beddard

PLATE VIII.

PLATE VIII.

Figs. 1, 2. Seeolis longicaudata.

Fig. 1. Male, dorsal surface.

Fig. 2. Male, ventral surface ; both figures enlarged about four diameters.

Figs. 3-5. SeROLIS SEPTEMCARINATA.

Fig. 3. Third thoracic appendage of male, left side.
Fig. 4. Base of penultimate joint of same appendage.
Fig. 5. One of the ambulatory limbs.

Figs. 6-16. Serolis pallida.

Fig. 6. Antenna of second pair.

Fig. 7. Antenna of first pair.

Fig. 8. Two joints of the filament witli sensory hairs ; more highly magnified.

Fig. 9. Mandible of left side, lower surface.

Fig. 10. Terminal portion of left side ; more highly magnified.

Fis;. 11. First maxilla of ris;ht side.

Fig. 12. Maxillipede of left side, lower surface.

Fig. 13. One of the second pair of thoracic appendages.

Figs. 14, 15. Spines from inner surface of penultimate joint of same appendage; more
highly magnified.

Fig. 16. Third thoracic appendage from right side of mnle.

The Voyage of H.M^S . Qiallenger"

Isopoda.Pl.Vin

Min.t tir. iirot- - lich

-2 SEROLIS LONGlCAUDATA.Beddard, 3-5 5ER0L1S SEPTEM CARI NATA , Miers .

6-ie. SEROLiS PALLl DA ,3eddapd.

'i.ATE IX.

{ZOOL. CUALL. EXP. — PART XXXIII. — 1S81.) — Klc.

PLATE IX.

Structure of the Eye.

Fig. 1. Surface view of membrane limiting the " ommateum" below ; a, perforations for
the nerve fibres arranged in groups of four, corresponding to each retinula ;
V, nuclei.

Fig. 2. Scmidiagrammatic .section through the eye of Serolis schytkei ; c, corneal lenses ;
■11, nuclei of Semper ; v, vitreous body ; r, retinula cells ; ^j, pigmentiferous
connective tissue corpuscles ; h, hyaline cells ; s, rhalxlom.

Fig. 3. Single element of the eye of Serolis cornuta, depigmented and isolated by
teasing; r, rhabdom ; /, its posterior filiform prolongation; h, hyaline cells;
n, their nuclei.

Fig. 4. Single element of the eye of Scrolls cornuta to show the pigment sheath sur-
rounding the rhabdom [r).

Fig. 5. Single element of the eye of Serolis schytkei ; r, rhabdom ; h, hyaline cell.

Fig. 6. One of the hyaline cells ; n, its nucleus.

Figs. 7, 8. Transverse section through the upper part of the retinula of Serolis schythti;
r, rhabdom ; 2^, pigment.

Figs. 9-15. A series of figures to show the varying form of the rhabdom in Seivlis
cormtta.

Figs. IG, 17. Transverse section through the upper part of tlie retinula of Serolis
cornuta ; r, rhabdom ; j?, its pigment sheath.

Figs. 18, 19. Two isolated retinula cells of Serolis schythei ; r, rhabdomcre.

Fig. 20. Series of transverse sections through retinula of Serolis schythei; a, nervous
rods below meml)rane ; h, lower end of retinula cell just above the pigmented
membrane ; c, retinula cells at the level of the nucleus (n) ; (/, four retinula
cells surrounding the hyaline cell (h) ; e, upper extremity of the retinula cells ;
(if), rlial)domere.

[lie Vo3'a,ge of ' H M S '■CKallenger':

Isopoda. PI . iX.

20 a.

D^ ^

20 1

20 c.

■1(1 1\

MiiLt-ern Bros UlVi.

STRUCTURE OF EYE

PLATE X.

PLATE X.

Structure of the Eye, &c.

Fig. 1. Single element of the eye of Serolis cornuta, depigmcuted by uitric acid ;
li, hyaline cell which has absorbed the pigment.

Fig. 2. Dissection of Serolis cornuta; h, heart; hej), hepatic CiBca ; ad, oviduct;
r, rectum.

Fig. 3. Diagrammatic transverse section through the eye of Serolis necera; n, nuclei of
Semper; I, vitreous body; (g) mass of cells below the vitreous body traversed
by a network of pigment.

Fig. 4. Masticatory stomach of Serolis schythei ; RP, LP, ribbed latertd plates ; /, la,
Ip, lateral ossicles ; 1, 2, 3, pyloric ossicles.

Fig. 5. Diagrammatic transverse section of eye of Scrolls hromleyana ; li, vitreous bodies ;
c, cornea ; m, tissue in which vitreous bodies are imbedded.

Fig. 6. Transverse section through the buccal region of Serolis seiitemcarinata ; a,
entrance to the buccal cavity ; m, mandible ; h, buccal cavity ; c, integument
bounding the lower surface of the body ; d, salivary glands ; e, connective
tissue cells ; n, nerve commissure.

Fig.^7. Embryo of Serolis antarctica; c, telson.

Fig. 8. Single element of the eye of Serolis necera isolated by teasing in glycerin ; v,
vitreous body with pigment sheath ; g, mass of cells below the vitreous body.

Fig. 9. Masticatory stomach of /So Wis Z)rom%an«; vu, cardiac ossicle ; F, ventral ossicle ;
RP, LP, ribbed lateral plates; /, la, Ip, lateral ossicles; 1, 2, 3, pyloric
ossicles ; s, opening of pylorus ; t, triangular ossicle.

Tlie Voyage of H . M. S "Challenger '

Isopoda PIX

ANATOMY OF SEROLIS

Minterrt Bros . lith .

cA

\y

900

/i