Life Sciences Contributions
Royal Ontario Museum
107
Redescription of Type Specimens of Species
of the Bryozoan Genera Monticulipora,
Mesotrypa, Peronopora, and Prasopora,
from the Upper Ordovician Rocks of
Toronto and Vicinity, Ontario, Canada
Madeleine A. Fritz
Digitized by the Internet Archive
in 2011 with funding from
University of Toronto
http://www.archive.org/details/redescriptionoftOOfrit
LIFE SCIENCES CONTRIBUTIONS
ROYAL ONTARIO MUSEUM
NUMBER 107
madeleine a. fritz Redescription of Type Specimens
of Species of the Bryozoan Genera
Monticulipora, Mesotrypa,
Peronopora, and Prasopora,
from the Upper Ordovician Rocks
of Toronto and Vicinity,
Ontario, Canada
Publication date: 26 April 1976
ISBN 0-88854-184-8
Suggested citation: Life Sci. Contr., R. Ont. Mus.
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Redescription of Type Specimens of Species
of the Bryozoan Genera Monticulipora,
Mesotrypa, Peronopora, and Prasopora,
from the Upper Ordovician Rocks of
Toronto and Vicinity, Ontario, Canada
Abstract
The species Prasopora donensis Parks and Dyer, Peronopora vera
Nickles and Mesotrypa distincta Parks have been previously
identified and described from the Upper Ordovician rocks of
Toronto and vicinity. The sub-species Monticulipora parasitica
multipora Dyer is herein accorded specific rank. The type speci-
mens of these species are redescribed using qualitative and quantita-
tive methods together with improved illustrations. A new species,
Prasopora richmondensis sp.nov., is described from the same strati-
graphic horizon.
Introduction
The Upper Ordovician rocks that underlie Toronto and vicinity are included in
the Georgian Bay Formation (Liberty, 1969). Prior to 1969 two formations were
recognized, namely, Dundas (Parks, 1924) and Meaford (Foerste, 1924). These
two formations were correlated respectively with the Maysville and Richmond of
Ohio. The Dundas Formation was divided by Parks (1924) and Dyer (1925) in
ascending order into the Rosedale, Danforth, Humber and Credit Members;
the Meaford into Erindale, Streetsville and Meadowvale Members. Parks and
Dyer (1922) described the Bryozoa of the Dundas Formation; Dyer (1925)
described the Bryozoa of the Meaford Formation. Armstrong (1945) studied in
greater detail the genus Stigmatella. Since the descriptions of the above workers
do not meet present standards, I began a study of the specimens which the authors
designated as types and which at present are located in the Department of
Invertebrate Palaeontology in the rom (Fritz, 1970, 1971, 1973, 1975). This study
has resulted in more detailed qualitative descriptions, in quantitative analyses,
and in improved illustrations. The present paper deals similarly with the type
specimens of species of the genera Mesotrypa, Monticulipora, Peronopora, and
Prasopora.
Materials and Methods
The specimens studied in this paper include:
Mesotrypa distincta Parks, 1925
Monticulipora parasitica multipora Dyer, 1925 (herein designated M. multipord)
Peronopora vera Nickles, 1905
Prasopora donensis Parks and Dyer, 1922
Prasopora richmondensis sp.no v.
In addition, the following type specimens have been kindly loaned to me for
comparison with the rom types:
Monticulipora multipora Utgaard and Perry, Indiana University, Hypotype No.
8252 (plus 8 micro sections of this Hypotype, Nos. 1051, 1284, 1388, 1599,
1645, 1646, 1647, 1648).
Peronopora vera Ulrich, United States National Museum, Holotype No. 43943.
Prasopora nodosa Ulrich, United States National Museum, Holotype No. 43691.
The external features of the zoaria (i.e., shape of the colony, character of the
surface) were observed with the aid of a hand lens, but the internal structures of
each species were determined by means of thin sections. While the descriptions
are two-dimensional, that is, as to what is seen in each of the standard views,
nevertheless, three-dimensional relationships of the interior of the colonies are,
to a certain extent, inferred. A study based on three-dimensional relationships is
outside the purpose of the present research. The mensuration of the number of
zooecia in 2 mm in the intermonticular areas and measurements in millimetres of
the maximum dimension of zooecial apertures in the monticular and inter-
monticular areas were made with the aid of a binocular microscope and a
micrometer scale calibrated to 0.01 mm. The number of entire mesopores and the
number of entire acanthopores in 1 mm 2 were obtained by using a compound
microscope and a reticle calibrated to 1 mm 2 . Statistical computations were made
on the ibm 370/165 computer at the University of Toronto Computer Centre.
As most of the samples had heterogeneous variances it was not possible to test
differences among means using parametric statistical methods. Instead, the
samples were tested for differences in dispersion using the non-parametric Mann-
Whitney U-test (Siegel, 1956). In the tables probability ranges associated with
significance tests are designated with asterisks as follows: *** = P < 0.001;
** = p < 0.01 ; * = P < 0.1 ; not significant = ns = P > 0.05.
Systematic Palaeontology
Order Trepostomata Ulrich, 1882a
Family Monticuliporidae Nicholson, 1879
Genus Monticulipora D'Orbigny, 1849
Description
Emended description of Monticulipora in Boardman and Utgaard, 1966.
Type Species
Monticulipora mammulata D'Orbigny, 1849: 25.
Monticulipora multipora Dyer, 1925
Fig. 1a, b
Monticulipora parasitica multipora Dyer, 1925: 71.
Monticulipora multipora — Utgaard and Perry, 1964: 43.
Original Description (Dyer, 1925)
Two specimens were obtained from the Streetsville member which appear to belong to
Monticulipora parasitica except for the fact that they possess numerous mesopores. In
this respect they agree with the form described and figured by Cumings from the Liberty
of Indiana, as belonging to this species. The apparent identity of our specimens with those
of Cumings and the constant departure from the type of the species, as indicated by the
presence of mesopores, seems to justify the creation of a new variety. The new variety
resembles M. cincinnatiensis, as stated by Cumings, but it differs in having acanthopores
and in the lower type of monticule.
Emended Description
Dyer designated two syntypes, rom 12168 and rom 12169. The following descrip-
tion of syntype 12168, now the lectotype of M. multipora, adds significantly to
that of Dyer (1925). Syntype 12169 is another species (to be considered later).
EXTERNAL FEATURES
Zoarium an overgrowth on a small dome-shaped mound of sediment and fossil
debris, 15 mm wide X 10 mm high, at the base of which a fragment of Isotelus
occurs. Thickness of zoarium 2 mm, surface of zoarium with prominent, conical
monticules, spaced 2 to 2.5 mm apart measuring from centre to centre.
TANGENTIAL SECTION
Zooecia subcircular to circular, 9 to 1 1 in 2 mm (Table 1). Zooecial wall granular,
knotty in appearance owing to irregular size of granules, 0.01 mm (or less) thick
below surface; 0.02 mm near surface and up to 0.03 mm in monticules, thin
zooecial lining, concentrically laminated, best observed near surface. Angular
mesopores varying in shape and size, from small to one-third size of zooecia,
surround most zooecia (Table 1). Acanthopores absent. In the wall, minute round
dots, with lucid centres, represent granules with clear interiors (Ulrich regarded
these lucid spots as acanthopores). Monticules with small mesopores interspersed
among zooecia which are larger than the zooecia in intermonticular areas, maxi-
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Fig. 1 a-b. Monticulipora multipora Dyer, lectotype rom 12168.
a. Longitudinal section, X48.6
b. Tangential section, X48.6
mum zooecial aperture in mm in monticules 0.18-0.26 (Table 1); maximum
diameter of zooecia in mm in intermonticular areas 0.13 - 0.20 (Table 1).
LONGITUDINAL SECTION
Zooecia either subprostrate or erect above base of zoarium, thereafter proceeding
directly to surface of zoarium. Walls thin throughout, knotty or minutely
wrinkled, owing to their granular nature, thin zooecial lining best observed in
younger part of section. Straight diaphragms and overlapping cystiphragms occur
in zooecia, their arrangement varies from half diaphragms and overlapping
cystiphragms near the surface to diaphragms only near surface, spaced one to
one-half tube diameter apart; cystiphragms usually in single series and in the
older part of zooecium, rarely in double series. Mesopores numerous and with
close-set diaphragms, commonly spaced one tube diameter apart. Acanthopores
absent.
Remarks
Monticulipora parasitica Ulrich, 1882b and Monticulipora parasitica multipora
Dyer, 1925 are similar in habit of growth, but in M. parasitica the zooecia are
angular and the monticules are composed of aggregations of small mesopores
surrounded by larger zooecia than those that occur in the intermonticular areas ;
furthermore, few mesopores occur in the intermonticular area.
Monticulipora epidermata Ulrich and Bassler, 1904 which shows affinities
with Monticulipora parasitica multipora Dyer, differs in that it forms small, low,
hemispherical masses to thin plate-like zoaria, which give off branches or knob-
like protusions; mesopores in inteimonticular areas are few and small, and mostly
confined to the centres of monticules.
Utgaard and Perry (1964: 43), although they did not examine Dyer's type,
identified and described his taxon from specimens collected from the Whitewater
Formation of eastern Indiana and western Ohio ; they referred to their specimens
as Monticulipora multipora. I have examined hypotype No. 8252 from Indiana
University and find that it is very similar to Dyer's type qualitatively. Quantita-
tively only a slight difference is noted in the maximum aperture diameter of the
zooecia in the intermonticular areas (Table 1). I therefore agree with Utgaard
and Perry that Dyer's variety should be given specific rank and known henceforth
as Monticulipora multipora.
Locality
Meaford Formation, Streetsville, Ontario.
Type
Lectotype rom 12168.
Mesotrypa Ulrich, 1893
Type Species
Diplotrypa infida Ulrich, 1886.
Mesotrypa distincta Parks, 1925
Fig. 2a, b
Mesotrypa (?) sp.nov., Parks and Dyer, 1922: 5.
Mesotrypa distincta Parks, 1925: 36.
Original Descriptions
Parks and Dyer's 1922 description of Mesotrypa (?) sp.nov. follows:
Of frequent occurrence on the Humber river is a discoidal bryozoan with a concentrically
wrinkled epitheca which may attain a diameter of 25 mm. The surface is gently convex
and practically smooth; the under side is correspondingly concave. The thickness varies,
and superposition of layers is not uncommon; a single layer is generally about one
millimetre thick.
The surface shows, in places, sub-quadrate zooecial openings more or less regularly
arranged and occurring to the number of nine in the space of two millimetres : in these
areas the walls seem to be in contact. In other parts of the surface the openings are
larger, more rounded, and separated by distinct interspaces although the zooecia are
never completely out of touch with each other.
Tangential sections show that the walls are moderately thick and independent even
where the mesopores are absent and the zooecial walls in close contact. Very small
acanthopores are sparingly developed. Vertical sections show the zooecial tubes to arise
with a slight slant from the basal plate and to proceed almost directly to the surface
with walls of practically the same thickness throughout. The zooecial tubes are crossed
by numerous irregular diaphragms for about two-thirds of their length ; the peripheral
third seems to be devoid of internal structures. The diaphragms are slanting and irregular
and occasionally simulate cystiphragms. Between the zooecial tubes are numerous
mesopores, crossed by close-set, horizontal diaphragms, which continue to the surface.
These mesopores show distinct evidence, in places, of narrowing towards the surface
of the polyzoarium.
Parks' description in 1925 of Mesotrypa distincta follows:
Numerous and better species of this discoidal bryozoan have been found since Part II
appeared. The description therein is accurate and needs little addition. Good vertical
sections show a most distinct pinching-out of the mesopores towards the surface. In
some cases, however, the mesopores continue to the surface with no diminution in
diameter. Shallow tangential sections show only occasional mesopores, the point at
which a mesopore might be expected to appear being occupied by an acanthopore. The
species is found at various levels on the Humber and abundantly at the Prison Farm
quarry.
Emended Description
Among the type material labelled Mesotrypa distincta, six syntypes are repre-
sented. The original description was based on only one of the syntypes, now
designated lectotype rom 1200hr. The remaining specimens were not sectioned
by Parks and Dyer but sections prepared for the present study verify the accuracy
of their identification. They become paralectotypes.
EXTERNAL FEATURES
Zoarium free, hemispherical, diameter 15 to 17 mm, 1.5 mm thick, slightly convex
above, base correspondingly concave with concentrically wrinkled epitheca;
surface with maculae flush with surface, normally 2.5 mm apart measuring from
centre to centre and consisting of zooecia larger than those in the intermacular
areas.
TANGENTIAL SECTION
Zooecia angular to subangular near surface, subcircular to circular below surface,
shape depending on number of mesopores present at a given depth, eight to nine
zooecia in intermacular areas (Table 2). Zooecial walls uniformly thin 0.01 mm in
general, 0.02 mm in maculae, concentrically laminated, laminae very fine, dis-
tinguishable best under magnification of X250; where two zooecia in contact a
dark area present formed from the combined laminae of the adjacent pair. Meso-
pores numerous in 1 mm 2 (Table 2) mostly rectangular, or triangular, more
numerous and larger at depth where they may surround zooecia in one or
two rows thus rendering zooecia circular to subcircular; mesopores become
smaller towards surface and at times peter out, leaving dense tips which might
suggest acanthopores, here zooecia become subangular to angular. Acanthopores
absent. Maculae composed of larger zooecia than those in intermacular areas,
some with large mesopores. Maximum apertural diameter of zooecia in mm in
macular areas 0.19-0.26 (Table 1); maximum apertural diameter in mm in
intermacular areas 0.14-0.16 (Table 2).
LONGITUDINAL SECTION
Zooecia and mesopores subprostrate for short distance, erect centrally, all
proceed directly to surface. Zooecial walls thin; diaphragms straight, curved,
oblique, infundibular, rarely cystoid, occur throughout zooecia, spaced one to
one and a half tube diameters apart. Mesopores singly or in groups of two or
three, many terminate before reaching zooecial surface; diaphragms uniformly
spaced, commonly 19 to 30 in 1 mm.
Remarks
The presence or absence of acanthopores is a distinguishing feature of Mesotrypa
species. M. discoidea Ulrich (1893: 260), M. quebecensis (Ami, 1892: 101),
Table 2. Measurements of the taxonomic characters of Mesotrypa distincta.
Measurements are given in millimetres. Figures in parentheses denote ranges.
n Mean ± S.E.
Number of zooecia in 2 mm in intermonticular area
Number of entire mesopores in 1 mm 2 in intermonticular area
Maximum apertural diameter of zooecia in monticules
Maximum apertural diameter of zooecia in intermonticular area 20
20
8.5 ± 0.10
(8-9)
20
22.5 ± 0.98
(16-31)
20
0.2 ± 0.006
(0.19-0.26)
20
0.2 + 0.003
(0.14-0.18)
B
Fig. 2 a-b. Mesotrypa distincta Parks, lectotype, rom 1200hr.
a. Longitudinal section, X48.6
b. Tangential section, X48.6
and M. rotunda Ulrich (1893: 262) from the Trenton all lack acanthopores, as
does M. distincta from the Humber Member, Dundas Formation; these four
species are similar when considered qualitatively, but no quantitative analysis is
available for the Trenton taxa. Mesotrypa diver sa (Fritz, 1971) from the Humber
Member has acanthopores; however the zoarial shape and surface configuration
of that species are unique among species known to the writer. M. patella (Ulrich,
1890: 458), M. orbiculoidea Cumings and Galloway (1913: 432), and M.
pauca Utgaard and Perry (1964: 69), all of Richmond age, have acanthopores.
Of these species, M. distincta resembles most closely M. patella except for the
absence of acanthopores in the former. Measurements of the taxonomic charac-
ters of M. distincta are recorded in Table 2; they may serve later in comparing
similar taxa unknown at present to me. In view of the combination of features
recognized in this taxon, I consider it to be a distinct species appropriately named
Mesotrypa distincta.
Locality
Dundas Formation (Humber Member), Humber River, Toronto, Ontario.
Types
Lectotype rom 1200hr; paralectotypes rom 30726.
Genus Peronopora Nicholson, 1881
Description
Description of Peronopora revised by Boardman and Utgaard (1966).
Type Species
Chaetetes decipiens Rominger, 1886.
Peronopora vera Nickles, 1905
Fig. 3a-d
Peronopora vera Ulrich, 1888, nomen nudum
Peronopora vera Nickles, 1905: 46
Peronopora vera Ulrich- Parks and Dyer, 1922: 7.
Description
Parks and Dyer (1922) described this material as follows:
This species is not uncommon in the quarry on the Don River and has often been
mistaken for Heterotrypa frondosa. The figures of tangential sections show the charac-
teristic appearance of true tangential section on the left-hand side; on the right-hand
side the section is deeper and slightly inclined showing both zooecial tubes and meso-
pores in inclined or longitudinal section. The vertical section, from a photomicrograph,
is shown without retouching in Plate n, Figure 5; it is rather confused owing to the
impossibility of cutting a section exactly parallel to the various elements. The drawing
was made by combining the most typical parts shown by the same thin section. The
median plane is marked by a very thin line on both sides of which appear the bases of
the zooecial tubes and of the mesopores which seem to alternate with a considerable
degree of regularity. The base of the zooecial tube is trapezoidal and small, that of the
mesopore is hexagonal and larger. The mesopores are crossed by crowded diaphragms
throughout: the zooecial tubes have diaphragms in the lower half and cystiphragms in
the upper.
10
Fig. 3 a-d. Peronopora vera Nickles, plesiotype, rom 1083hr.
a. Tangential section, X48.6 c. Longitudinal section, X48.6
b. Longitudinal section, X48.6 d. Tangential section, X48.6
11
Emended Description
Specimen, fragment of a subfrondescent, bifoliate zoarium, covers an area of
45 by 25 mm with maximum thickness of 2 mm; a few small, rounded, irregularly
spaced protuberances that rise above the surface, varying in size, may represent
aborted branches. Surface with low monticules composed of zooecia larger than
those in intermonticular areas. Acanthopores, blunt to somewhat pointed,
protrude beyond the surface.
TANGENTIAL SECTION
Zooecial apertures near surface round to subangular, seven to eight in 2 mm
(Table 3). Zooecial walls thin, 0.01 mm (or less) in deep sections, 0.02 to 0.03 mm
at surface, and up to 0.04 mm in monticules, concentrically laminated. Mesopores
numerous, surround zooecia (Table 3), angular to subangular, vary ng in size
and shape, some with an areal extent close to that of certain zooecia, occasionally
a cluster of mesopores in monticules. Acanthopores numerous, locally inflecting
(Table 3), varying in diameter from 0.02 to 0.05 mm depending on where section
cuts the structure, central lumen, surrounded by concentric laminae, lumen at
times obscured by pyrite deposit. Monticules with larger zooecia than in inter-
monticular areas. Maximum apertural diameter of zooecia in monticular areas
in mm 0.19-0.27 (Table 3); maximum apertural diameter of zooecia in inter-
monticular areas in mm 0.14-0.19 (Table 3).
LONGITUDINAL SECTION
Zooecia prostrate for short distance on either side of mesotheca, then becoming
erect to zoarial surface, or they may be erect to the surface from the outset;
mesotheca with median lamella. Zooecial walls thin, laminae thickening slightly
towards surface, lam nae convex outward, steeply inclined and merging with
diaphragms and cystiphragms, and with diaphragms in mesopores. Diaphragms
in zooecia straight, curved, or sigmoidal, commonly in immature zone, spaced
one-quarter to one-half tube diameters apart and followed on distal wall by
overlapping cystiphragms, in longer zooecia from six to nine diaphragms and
cystiphragms occur. Above the immature zone, mesopores, mostly erect to surface,
contain closely and regularly arranged, usually straight diaphragms. Acantho-
pores numerous, usually observed in wall, but at times seen to cross a zooecium
obliquely, wall relatively coarsely laminate, laminae convex outward and diverg-
ing at a low angle from central lumen, then passing into diaphragms and cysti-
phragms.
Remarks
In 1888, Ulrich named Peronopora vera but he did not describe or figure it. His
type No. 43943, with accompanying thin sections, is in the United States National
Museum. Donald Dean has kindly loaned this material to me for comparison
with Parks and Dyer's plesiotype. I find that the two are similar qualitatively
and that no significant difference occurs quantitatively (Table 3).
Locality
Dundas Formation, Upper Ordovician, Don Valley Quarry, Toronto, Ontario.
Type
Plesiotype rom 1083hr.
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Prasopora Nicholson and Etheridge, 1877
Description
The description of Prasopora may be found in Ross (1970).
Type Species
Prasopora grayae Nicholson and Etheridge, 1877
Prasopora donensis Parks and Dyer, 1922
Fig. 4a-c
Original Description (Parks and Dyer, 1922)
The zoarium of this species is circular and free, probably with a concentrically wrinkled
epitheca. The diameter ranges from 17 to 20 mm and the thickness is approximately one
millimetre. The upper surface is gently convex and the under surface correspondingly
concave. The celluliferous surface shows that the ordinary apertures are arranged in
quincuncial rows springing from a number of very ill-defined centres. They are usually
hexagonal in outline and occur to the number of four in the space of one millimetre. At
intervals of 2.5 to 3 mm are clusters of larger cells, and at about the same interval occur
slightly defined monticules. The clusters and the monticules are not necessarily coincident
nor are they necessarily the centres of the quincuncial systems.
Tangential sections show that the ordinary zooecial tubes are nearly or quite circular
but that they become elliptical as the centres of the clusters are approached. The walls
of the zooecial tubes are comparatively thin and independent, touching each other in
the direction of the rows but separated in other directions by a number of large angular
mesopores. Cystiphragms appear in nearly every tube. Acanthopores are scarcely to be
discerned but there is some evidence of very small ones at the points of junction of
the tubes.
Vertical sections, where ideally cut, show about five well-developed cystiphragms and
clearly defined diaphragms in the zooecia, the latter being confined to the lower part
of the tube. The mesopores are crowded with diaphragms.
This species has decidedly the surface characteristics and manner of growth of the
genus Aspidopora and approaches very closely to Aspidopora newberri [sic] Nicholson.
We would without hesitation, ascribe the species to Aspidopora were it not for the
undoubted diaphragms in the zooecial tubes.
Except for the somewhat larger size, the species closely resembles Prasopora lenticu-
lar is Ulrich. The vertical sections are almost identical, but the tangential section of
P. lenticularis shows a closer spacing of the zooecial tubes and a less development of
mesopores. The arrangement of the zooecial tubes in rows is apparently a feature of
both species.
Emended Description
Six very poorly preserved specimens are listed as syntypes of Prasopora donensis.
Only two warrant redescription and become the lectotype and paralectotype.
Three are designated Prasopora cf. donensis, and one represents the brachiopod
Trematis millepunctata Hall.
EXTERNAL FEATURES
Zoarium a small, free discoidal mass adhering to matrix, larger specimen before
sectioning, 17 mm in diameter, a little over 1 mm in height; slightly convex above
concave below, concentrically wrinkled epitheca recognized only by impression
on matrix of a small portion of the base; monticules almost flush with surface,
2.5 to 3 mm apai «. measuring from centre to centre, zooecia in inter-areas quincun-
cially arranged.
14
Fig. 4 a-c Prasopora donensis Parks and Dyer, lectotype, rom 1084hr.
a. Tangential section, X24.3
b. Tangential section, XI 2.2
c. Longitudinal section, X24.3
15
TANGENTIAL SECTION
Zooecial apertures oval to circular, commonly 8 to 9 in 2 mm (Table 4). Zooecial
wall thin 0.01 mm (or less) in width, finely laminated, individual laminae dis-
tinguishable only under magnifications of X250 or higher. Ordinary zooecia
surrounded by numerous angular mesopores, mesopores in 1 mm 2 19 to 37
(Table 4), some one-third to one-half size of a zooecium, only rarely do zooecia
come in contact, acanthopores absent, cystiphragms in most zooecia. Monticules
composed of zooecia larger than those in intermonticular areas and with inter-
spersed mesopores, maximum diameter zooecial aperture in monticular areas in
mm 0.26-0.31 (Table 4); maximum diameter zooecial aperture in intermonticular
areas in mm 0.13-0.19 (Table 4).
LONGITUDINAL SECTION
Zooecia, slightly recumbent in peripheral zone, erect in central area, intersect
zooecial surface approximately at right angles. Zooecial walls finely laminate,
distinct under high magnification, in best preserved sections five cystiphragms on
one side only, large at base, diminishing in size towards surface, basal cysti-
phragms may extend half way (or even farther) across a zooecium ; straight or
oblique diaphragms, corresponding in number to cystiphragms, extend from
cystiphragms to opposite zooecial wall.
Remarks
P. donensis is significantly different from P. richmondensis sp.nov. (description
to follow) externally in that it lacks the conspicuous nodular surface of that
species; internally in the absence of acanthopores, the presence of more numerous
mesopores, and smaller zooecia in the intermonticular areas.
Closely related to P. donensis is P. lenticuJaris Ulrich (1893: 253), from the
Black River (Decorah) of St. Paul, Minnesota. The zoarium of the latter taxon
is parasitic, a feature which may not be significant. P. lenticularis has somewhat
smaller zooecia and only a single mesopore between the zooecia in the inter-
monticular areas, a sharp contrast to the numerous mesopores in the same areas
in P. donensis. Owing to the extremely poor preservation of types some doubt
exists as to the generic reference.
Locality
Dundas Formation, Don Valley Quarry, Toronto, Ontario.
Types
Lectotype rom 1084hr, paralectotypes rom 32317 and 32318.
16
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Prasopora richmondensis sp.nov.
Fig. 5a-c
Monticidipora parasitica multipora Dyer. 1925: 71.
Description
Dyer (1925) included the specimen rom 12169, herein described, among the
syntypes of Monticidipora parasitica multipora. He must have based his identifica-
tion upon the somewhat similar nodular surface of the zoarium of his variety.
Thin sections prepared from the specimen for this revision indicate that it repre-
sents the new species P. richmondensis.
EXTERNAL FEATURES
Zoarium an irregular shaped mass, part of which encrusts the brachiopod
Hebertella or Platystrophia. Specimen 15mmX 17 mm, greatest thickness
1.75 mm, petering to 1mm at periphery. Surface with prominent irregularly
spaced unequal monticules, the smaller of which are conical, others larger and
stouter, still others coalesce to form elongate elevations.
TANGENTIAL SECTION
Zooecia mostly circular but slightly angular near surface, commonly 8 to 9 in
2 mm (Table 5), zooecial walls thin, concentric laminae only faintly distinguish-
able, walls generally less than 0.01 mm thick below surface, 0.01 to 0.02 mm near
surface. Mesopores, small and angular, rarely one-third size of zooecia, surround
most zooecia (Table 5) and less abundant where zooecia are subangular. Acantho-
pores moderately abundant (Table 5), 0.02 to 0.05 mm in diameter with small
lumen surrounded by dark concentric laminae, occasionally acanthopores indent
zooecial aperture. Monticules composed of larger zooecia than in intermonticular
space and with interspersed mesopores. Cystiphragms occupy from one-half to
one-third area within each zooecium. Maximum apertural diameter of zooecia
in monticules in mm 0.26-0.31 (Table 5); maximum apertural diameter of
zooecia in intermonticular areas 0.18-0.22 mm (Table 5).
LONGITUDINAL SECTION
Zooecia arise directly from the brachiopod and free basal portion and continue
in a straight course to the surface of the zoarium. Walls uniformly thin through-
out. Each zooecium with cystiphragms and straight diaphragms in regular
sequence throughout their length, within space of 1.75 mm 12 cystiphragms and
12 diaphragms occur. Acanthopores with clear central area, flanked by fine
laminae, appear at various levels through the entire growth.
Remarks
P. richmondensis sp.nov. may be distinguished from P. donensis Parks and Dyer
by the conspicuous nodular surface, by the presence of acanthopores, and by
fewer mesopores. The taxon is similar to P. nodosa Ulrich (1882b: 245) in external
appearance, although Ulrich did not consider the zoarium to be parasitic.
Through the courtesy of R. S. Boardman and D. A. Dean of the United States
National Museum, I have been privileged to examine Ulrich's syntypes of
P. nodosa (usnm 43691) from the Trenton (Cathys Limestone), Nashville, Ten-
18
Fig. 5 a-c. Prasopora richmondensis sp.nov., holotype, ROM 12169.
a. Longitudinal section, X48.6
b. Tangential section, X48.6
c. Tangential section, X48.6
19
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nessee. The two are similar externally and in the number of zooecia in 2 mm in the
intermonticular areas. The monticules, however, are dissimilar; in P. nodosa
numerous tiny, angular mesopores, varying in shape and size, surround the
zooecia or form elongate, stellate, or irregular aggregations. Ulrich states that
"a moderate number of spiniform tubuli may be observed in tangential sections".
I fail to distinguish these structures in his sections. It is possible he confused them
with the solid ends of pinched-out mesopores. No acanthopores are visible in his
longitudinal sections.
To describe a new species on a single specimen is admittedly a weakness, nor
have I been able to locate a comparable species from a similar stratigraphic
horizon after a careful perusal of the pertinent literature available to me. As
pointed out in the preceding paragraph, Prasopora nodosa Ulrich from the Middle
Ordovician (Trenton) is the closest species with which Prasopora richmondensis
may be compared. It is conceivable that Prasopora richmondensis is an evolution-
ary derivative of that older taxon.
Locality
Meaford Formation, Streetsville, Ontario.
Type
Holotype rom 12169.
21
Acknowledgments
Thanks are expressed to Janet Waddington, Curatorial Assistant, Department of
Invertebrate Palaeontology, rom, for calculating the Mann-Whitney U Statistics;
to Huibert Sabelis for the restoration of original thin sections and for the prepara-
tion of new sections required for the research; to Joan Burke for her valued
secretarial assistance and for typing the manuscript.
The photographs were taken by Mr. Brian O'Donovan, Department of Geology,
University of Toronto.
22
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23
NICHOLSON, H. A. and R. ETHERIDGE, JR.
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24
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