Life Sciences Contributions 1 1 1
Royal Ontario Museum

Redescription of Type Specimens

of Species of the Bryozoan Genera
Atactoporella, Homotrypa, and Homotrypella,
from the Upper Ordovician Rocks of the

Credit River Valley, Ontario, Canada

Madeleine A. Fritz

preety

ROM

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MADELEINE A. FRITZ

LIFE SCIENCES CONTRIBUTIONS
ROYAL ONTARIO MUSEUM

NUMBER 111

Redescription of Type Specimens
of Species of the Bryozoan Genera
Atactoporella, Homotrypa,

and Homotrypella, from

the Upper Ordovician Rocks

of the Credit River Valley,
Ontario, Canada

Publication date: 6 July 1977

ISBN 0-88854-199-6

ISSN 0384-8159

Suggested citation: Life Sci. Contr., R. Ont. Mus.

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Redescription of Type Specimens
of Species of the Bryozoan Genera
Atactoporella, Homotrypa,

and Homotrypella, from

the Upper Ordovician Rocks

of the Credit River Valley,

Ontario, Canada

Abstract

Bryozoan species from the Upper Ordovician Georgian Bay (Meaford)
Formation (Atactoporella densa Dyer, Atactoporella peculiaris
(Dyer), Homotrypa creditensis (Dyer), Homotrypa streetsvillensis,
and Homotrypella hospitalis Nicholson) are redescribed using the fol-
lowing criteria: number of zooecia in 2 mm in intermacular area,
number of entire mesopores in | mm? in intermonticular area, maxi-
mal apertural diameter of zooecia in maculae, and maximum apertural
diameter of zooecia in the intermacular area.

Introduction

This is the sixth publication of a series devoted to the redescription of trepostomatous
bryozoan types from the Upper Ordovician rocks of Toronto and vicinity that are
located in the Department of Invertebrate Palaeontology of the Royal Ontario
Museum (Fritz, 1970, 1971, 1973, 1975, 1976a). The present paper deals with
species of the genera Atactoporella, Homotrypa, and Homotrypella described by
Dyer (1925) from outcrops in the Credit River Valley a few miles west of Toronto;
these rocks were formerly included in the Meaford Formation (Foerste, 1924), but are
now included in the Georgian Bay Formation (Liberty, 1969).

Materials and Methods

The primary types of the following species are treated in this paper:
Atactoporella densa Dyer (1925)

Atactoporella peculiaris (Homotrypella hospitalis peculiaris Dyer, 1925)
Homotrypa creditensis Dyer, 1925

Homotrypa streetsvillensis Dyer, 1925

Homotrypella hospitalis (Nicholson, 1881) (Homotrypella expansa Dyer, 1925)

In addition, the following are also studied:
Atactoporella multigranosa (Ulrich, 1879) — holotype 43626 USNM
Atactoporella newportensis Ulrich, 1883 — cotypes 43627 and 40193 USNM
Homotrypa austini Bassler, 1903 — cotype 41762 USNM
Homotrypa communis Bassler, 1903 — cotype 41755 USNM

The external features of the zoaria (1.e., shape of the colony, character of the
surface) were observed with a hand lens, but the internal structures of each species
were determined by means of thin sections. 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 intermonticular
areas were made with 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? were obtained by using a compound microscope and a reticle calibrated to
1 mm?. Statistical computations were made on the 1BM 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, proba-
bility ranges associated with the significance tests are designated with asterisks as
follows. “** =P =0 00k =" =P =0.0l) * =P = 0101 nor ‘sitemiineant
=ns=P > 0.05.

Systematic Palaeontology

Order Trepostomata Ulrich, 1882a
Family Monticuliporidae Nicholson, 1881

Genus Atactoporella Ulrich, 1883

Type Species
Atactoporella typicalis Ulrich, 1883: 248-250.

Atactoporella densa Dyer (1925)

Fig. 1A-B

Original Description (Dyer, 1925)

‘‘A single specimen of a bryozoan, showing the internal characters of the genus Atactoporella,
was found in the zone of Bythopora meeki in the Streetsville member. It is not well preserved,
but it differs so decidedly from any previously described member of the genus from the
Cincinnatian series that it has been decided to erect a new species for its reception.

‘‘The zoarium consists of four superimposed layers, which are rather thick for the genus,
each layer varying from two to three millimetres in a vertical direction. It could not be
ascertained, on account of the poor preservation of the fossils, whether the surface is mon-
ticulose or smooth. It apparently is not an incrusting form.

‘‘In characters shown by both tangential and vertical sections, A. densa resembles A. ortoni

a

(Nicholson), of the Maysville of Ohio. The tubes are small, nine to ten in two millimetres, with
the comparatively thick walls lined by average-sized acanthopores. As many as twelve acan-
thopores have been counted surrounding a single zooecial tube. The mesopores, so far as can
be determined, are not as numerous as in A. ortoni, and are not filled by secondary deposits as
in that species, but are open throughout their length. The mesopores are crossed by numerous
diaphragms, while the zooecia have both diaphragms and cystiphragms.

‘‘In addition to the differences already enumerated, A. densa differs from A. ortoni in the
manner of growth. The latter species forms exceedingly thin, monticulose crusts, usually
attached to the shells of brachiopods. The Streetsville form differs from A. schucherti, Ulrich,
the only other member of the genus found in the Richmond, in the much smaller size of the
acanthopores, in the smaller number of mesopores, and in the manner of growth.’’

Emended Description

EXTERNAL FEATURES

Dyer based his description on a single, roughly dome-shaped specimen (now frag-
mented), approximately 10 mm wide at base X 15 mm high; surface with small,
round monticules 2 mm to 2.5 mm apart measuring from centre to centre. Acantho-
pores protrude beyond surface of zoarium. Polished surfaces now available through
the specimen from top to bottom revealed a previously unsuspected symbiotic
stromatoporoid—bryozoan sequence beginning on the coenosteum of a young
stromatoporoid. Three successive growths appear in the sequence measuring respec-
tively | mm, 2 mm, and 3 mm in maximum thickness.

During the course of my research, another example of A. densa was identified,
providing further evidence of the validity of Dyer’s species. This specimen occurs in
the symbiotic sequence referred to in the description of Homotrypella hospitalis
(p.19) and has a maximum thickness of 3 mm. This biocoenosis was described under
the title ‘‘A Microbioherm’’ (Fritz, 1976b).

TANGENTIAL SECTION

Zooecia subangular to circular, 8.5 to 11 in 2 mm in intermonticular areas (Table 1),
adjacent to or separated by microcrystalline deposits of varying extent. Walls of
adjacent zooecia amalgamate or with a dense median line; width of amalgamate walls
0.01 mm (or less) to 0.02 mm, in monticules slightly thicker, walls with fine concen-
tric laminae, laminae distinct only in magnifications <x 150 or more. Mesopores few,
round or angular (Table 1). Acanthopores prominent with relatively large lumen,
moderately numerous (Table 1), composed of concentric laminae and situated mostly
in subangular portions of zooecia, slightly inflecting zooecial apertures rendering
them subpetaloid in shape, diameter 0.01 to 0.05 mm; small crystalline granules,
which stud zooecial walls between acanthopores, might be taken for small acantho-
pores, but that they are not typical acanthopores is discussed in the following lon-
gitudinal section. In monticules, diameter of zooecia in mm in monticular areas 0.15
to 0.19 (Table 1), in intermonticular areas 0.07 to 0.10 (Table 1).

LONGITUDINAL SECTION

Zooecia subprostrate for a short distance above base of zoarium, becoming erect to
periphery or erect throughout their entire course. Walls thin, thickening slightly
towards surface. Diaphragms horizontal, diagonal, or V-shaped, spaced one-quarter
to one tube diameter apart, extend across at least two-thirds of zooecial apertures and
rest upon cystiphragms. Cystiphragms relatively small, bulbous, and overlapping,

line zooecia throughout their length. Mesopores few with diaphragms one-half to one
tube diameter apart, some of which gradually disappear at surface. Acanthopores, of
relatively coarse laminae that diverge at low angle and pass into diaphragms and
cystiphragms; at close of each growth stage, acanthopores protrude beyond the sur-
face as solid rods of dense laminae. The small crystalline granules mentioned in the
tangential section can be traced in linear series along cut edges of zooecial walls or
where a section grazes a fragment of wall. These structures, a very distinctive feature
of this species, may represent crystal-filled pores, although no sign of an enclosing
wall is evident, or they may represent specialized, residual acanthopores.

Remarks

Atactoporella densa and A. peculiaris are very closely related. Comparisons of these
and other species of the genus together with their relationships are summarized in the
‘*Remarks’’ following the description of A. peculiaris.

Locality
Meaford Formation, Streetsville, Ontario.

Type
Holotype ROM 12148; hypotype ROM 254HR (with Homotrypella hospitalis).

Atactoporella peculiaris (Dyer)

Figs. 1C_D, 2A-B
Homotrypella hospitalis peculiaris Dyer, 1925: 69, 70.

Original Description (Dyer, 1925)

‘‘H. hospitalis is abundant in all the subdivisions of the Richmond formation on the Credit
River, with the exception of the Queenston. At times it forms very regular, hemispheric or
sub-conical zoaria, while at other times the zoaria are very irregular in shape. In addition, a few
specimens have been ascribed to a new variety.

‘“‘H. hospitalis peculiaris differs from the type in one feature only, namely, in the possession
of numerous minute acanthopores, which are situated along the zooecial walls between the
large acanthopores, characteristic of the type. These small acanthopores are much more pro-
nounced near the surface of the zoarium, where as many as six have been counted between two
large acanthopores. Deeper in the zoarium they may disappear altogether. They are apparently
of the nature of true acanthopores since hollow centres have been seen in many instances.”’

Fig. | A-B. Atactoporella densa Dyer, holotype, ROM 12148.
A. Tangential section, 60.
B. Longitudinal section, 30.
C-D. Atactoporella peculiaris (Homotrypella hospitalis
peculiaris Dyer), holotype, ROM 12166.
C. Tangential section, x30.
D. Longitudinal section, x30.

8

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Emended Description

EXTERNAL FEATURES

Zoarium lobate with semi-ramose or nodular protrusions, holotype 25 mm wide,
15 mm in height, surface with low monticules about 2 mm to 2.5 mm apart measur-
ing from centre to centre, consisting of larger zooecia than in intermonticular areas;
acanthopores protrude beyond zoarial surface.

TANGENTIAL SECTION

Zooecia 8 to 10 in 2 mm in intermonticular areas (Table 1), adjacent to or separated
by microcrystalline deposits; walls of adjacent zooecia amalgamate or with a median
dark line, width of amalgamated walls 0.01 mm (or less) to 0.02 mm, a little thicker
in monticules; walls finely laminate, laminae detected only under magnifications
x 150 or more. Mesopores few (Table 1), small, round, triangular or quadrangular.
Acanthopores prominent, relatively numerous (Table 1), at times slightly inflecting
zooecia, rendering aperture irregular in shape, diameter 0.02 mm to 0.06 mn, large
lumen surrounded by dense laminae. Small crystalline granules stud zooecial walls
between acanthopores; these structures occur also in Atactoporella densa (p. 2).
Diameter of zooecial aperture in monticular areas 0.23 mm to 0.28 mm (Table 1),
0.14 to 0.20 mm in intermonticular areas (Table 1).

LONGITUDINAL SECTION

Zooecia subprostrate for a short distance above base, then erect, intersecting zoarial
surface at approximately right angles; walls thin, fine laminate, straight or slightly
undulating in axial region, then gradually thickening from base of peripheral region
to surface; granules in linear arrangement present in parts of ideally cut section.
Horizontal diaphragms in axial region, one to three tube diameters apart, closer from
subperipheral region to surface, where 13 may occur in space of | mm. Globose
cystiphragms, at times overlapping, occur on the distal walls throughout post-axial
region; larger cystiphragms often present on proximal wall. Diaphragms rest either
distally, medially, or proximally upon cystiphragms. Mesopores with close-set dia-
phragms, more numerous in deep sections, may gradually disappear as growth pro-
ceeds. Acanthopores prominent, with large central tube flanked by relatively coarse
laminae that diverge at a low angle and pass into diaphragms and cystiphragms.

Remarks

Atactoporella densa and Atactoporella peculiaris, each with granular walls, are
closely related species, although the smaller zooecia and more compact skeletal
structure of A. densa distinguish it qualitatively from A. peculiaris, which has
larger zooecia and a more open framework. Furthermore, as far as known, A. densa
forms incrusting, symbiotic.zoaria whereas: A. peculiaris forms lobate zoaria from

‘which extensions protrude, resembling aborted branches. Quantitatively the two are

compared in Table 1, which shows that they differ significantly in the maximum

Fig. 2 A-B. Atactoporella peculiaris (Homotrypella hospitalis
peculiaris Dyer, hypotype, ROM 12275.
A. Tangential section, x60.
B. Longitudinal section, x30.

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apertural diameter of the zooecia in intermonticular areas and in the maximum aper-
tural diameter of zooecia in monticular areas.

From an examination of Ulrich’s holotype USNM 43626 of Atactoporella multi-
granosa from the Upper Ordovician, Maysville (Fairmount) Hamilton, Ohio, I believe
it to be a near ancestor of A. densa; however, the larger acanthopores and more
numerous granules are distinctive features of Dyer’s species.

From a study of Ulrich’s cotypes of Atactoporella newportensis USNM 43627 and
40193 from the Upper Ordovician, Eden Formation of Newport, Kentucky, I con-
sider that species to be a forerunner of A. peculiaris. These two species agree in the
lobate-ramose nature of the monticulose zoarium and in the size and shape of the
zooecia. However, Ulrich did not differentiate in the size of acanthopores and
granules which he lumped under the term ‘“‘spiniform tubuli’’. In A. peculiaris the
acanthopores are considerably larger than the granules; the latter are distinguishable
in longitudinal sections as linear rows of pores.

Atactoporella schucherti Ulrich (1883) from the Richmond of Ohio differs from A.
densa and A. peculiaris in that it possesses large inflecting acanthopores and lacks
granules.

Atactoporella spicata Bassler (1928) from the late Upper Ordovician, Ellis Bay
Formation of Anticosti Island, differs from Dyer’s species in having thick zooecial
walls inflected by prominent acanthopores between which are numerous relatively
large granules, which often appear in sections as double rows.

Atactoporella irregularis Boulange (1963) from the Upper Ordovician of
Montagne-Noire has circular zooecia separated by large angular mesopores, few
acanthopores, and an absence of granular walls. This combination of features seems
to preclude its inclusion in the genus Atactoporella.

Atactoporella depressa Astrova (1957) from the Silurian of Russia also lacks the
granular structure of the genus according to the author’s figures. She states that her
species most closely resembles A. typicalis Ulrich (1883) from the Eden Formation of
Kentucky, a formation that is considered equivalent to the Dundas Formation of
Toronto.

Locality
Meaford Formation, Streetsville, Ontario.

Type
Holotype ROM 12166, hypotype RoM 12275.

Genus Homotrypa Ulrich, 1882b

Type Species
Homotrypa curvata Ulrich, 1882b: 242-243.

Homotrypa Ross, 1970.

Regarding the genus Homotrypa, a taxonomic problem arose in 1920 when Vinassa
de Regny proposed two new genera, Cadornipora and Gortanipora, to which he

referred certain species long thought to belong to Homotrypa. Vinassa de Regny cited
Homotrypa nodulosa Bassler (1903) as genotype of Cadornipora and Homotrypa
bassleri Nickles as genotype of Gortanipora. Bassler (1953) regarded Cadornipora
as a junior synonym of Homotrypa but Gortanipora, with ‘‘hook-shaped’’ cysti-
phragms characteristic of the genotype H. bassleri, he considered to be a valid genus.

Utgaard and Perry (1964) discussed this problem at considerable length in their
study of the Whitewater fauna, which has much in common with that of the Credit
River. They concluded by stating, ‘‘We prefer to recognize only the genus
Homotrypa pending further elucidation of the generic features of Gortanipora.”’

Dyer’s species redescribed herein possess only ‘‘hook-shaped’’ cystiphragms
characteristic of Gortanipora. I agree with Utgaard and Perry that Gortanipora is not
an acceptable genus as it is at present described. Dyer’s species are therefore retained
in the genus Homotrypa.

Homotrypa creditensis Dyer, 1925
Fig. 3A-B

Original Description (Dyer, 1925)

‘*This member of the Homotrypa communis group of Bryozoa occurs in the zone of Homotrypa
streetsvillensis, in association with the type species of the zone. H. creditensis is the only
member of the genus in the Credit River section which bears monticules. These are distributed
regularly over the surface of the zoarium with an average distance of three millimetres between
them. Their character cannot be determined by an examination of the surface, but tangential
sections show them to be composed of mesopores, surrounded by zooecial tubes of almost
twice the average size.

‘‘In tangential sections, the zooecial tubes are seen to be small, twelve occurring in two
millimetres. Their walls are thin for the greater part of their course but appear thicker near the
surface of the zoarium, as the mesopores in this part are filled with a secondary deposit of
calcite. Numerous angular mesopores are scattered throughout the zoarium as well as being
grouped into the monticules as mentioned above. Acanthopores are present but are small and
unimportant.

‘In vertical sections, it is seen that cystiphragms only are present in the zooecial tubes. They
are restricted to the younger part of the mature region, both zooecia and mesopores being
empty near the surface. Closely crowded diaphragms are found in the mesopores.

‘“‘H. creditensis is closer to H. nodulosa, Bassler, than to any other form, these two species
being very similar in vertical sections, but differing decidedly in tangential sections, and in
growth.”’

Emended Description

EXTERNAL FEATURES

Zoarium ramose, branches dichotomous, cylindrical to slightly compressed, max-
imum diameter 7 mm tapering to 4 mm. Surface with conical monticules, spaced 2 to
2.5 mm apart measuring from centre to centre.

Fig. 3 A-B. Homotrypa creditensis Dyer, holotype, ROM 12162.
A. Tangential section, «30.
B. Longitudinal section, 30.

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TANGENTIAL SECTION

Zooecia round or oval, rarely angular, commonly 10 to 12 in 2 mm (Tables 2, 3);
wall moderately thick, at surface 0.03 mm to 0.05 mm, reaching 0.07 mm in mon-
ticules; composed of homogeneous, concentrically arranged laminae, at times show-
ing dark central band. Mesopores in intermonticular areas mostly small and angular
(Tables 2, 3). Acanthopores moderately abundant, small, non-inflecting, 0.02 mm to
0.03 mm in diameter with central lumen flanked by close-set concentric laminae
(Tables 2, 3). Monticules with small to relatively large angular mesopores varying in
size and surrounded by larger zooecia than those in intermonticular areas; in certain
monticules, acanthopores more numerous than in intermonticular areas. In mon-
ticules, apertural diameter of zooecia 0.14 to 0.20 mm (Tables 2, 3); in intermonticu-
lar areas apertural diameter 0.07 to 0.15 mm (Tables 2, 3).

LONGITUDINAL SECTION

Zooecia curve outwards from axial region at an angle of approximately 45°, opening
somewhat obliquely at zoarial surface. Zooecial wall thin, slightly crenulated in axial
region, thickening in subperipheral zone, becoming progressively thicker and some-
what moniliform towards periphery. Wall laminae in outer peripheral region broadly
convex outwards, sharply convex outwards in innermost part of that region where
central line of demarcation often visible; laminae then diverge at a low angle from
central area to continue into zooecial diaphragms and cystiphragms and into dia-
phragms of mesopores. Diaphragms throughout axial region spaced two to three or
four tube diameters apart, ‘‘hook-shaped’’ cystiphragms on proximal wall followed
distally by one or two flat diaphragms. Mesopores in groups in peripheral zone (1.e.,
where section passes through a monticule) or otherwise mostly single; diaphragms
closely spaced and thicker than those in zooecia. Acanthopores few, indistinctly
visible in peripheral region, some cutting diagonally across zooecia; structure of
acanthopores not clear.

Remarks

The genus Homotrypa, as already noted, is represented in the Upper Ordovician by a
number of very closely related taxa, referred to as species, with slight morphological
differences. In this case, as with other genera considered in this series of publications
(Fritz, 1970, 1971, 1973, 1975, 1976a), discussion has centred upon populations
(possibly interbreeding) which have been subjected to successive pressures resulting
in minor morphological features which may or may not represent genetic mutations.
As more intergrading taxa become known it may become possible to assess their true
biological relationships.

Dyer (1925) compared Homotrypa creditensis with Homotrypa nodulosa Bassler
(1903). Qualitatively, the two species resemble one another in the shape and mon-
ticuled surface of the zoarium. H. creditensis differs, however, in having small
zooecia and fewer acanthopores of uniform size. Utgaard and Perry (1964) examined
Bassler’s cotype no. 41758 of H. nodulosa from the United States National Museum.
Table 2 is a comparison of the data published by Utgaard and Perry with the meas-
urements of H. creditensis obtained in the present study. Quantitatively, the two
species differ insignificantly in the number of zooecia in 2 mm in intermonticular
areas, but differ very significantly in the maximum apertural diameter of zooecia in

12

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14

monticules (Table 2) and in the apertural maximum diameter in the intermonticular
areas (Table 2).

Homotrypa austini Bassler (1903) is a close relative of H. creditensis in the size
and shape of the ramose zoarium, although H. austini has a macular rather than
monticuled surface. Each of these two species possesses ‘‘hook-shaped’’ cysti-
phragms. I have examined Bassler’s cotype no. 41762 from the USNM collections and
have made measurements that permit the quantitative comparison of H. austini and
H. creditensis (Table 3) in which the two differ insignificantly in the number of
zooecia in 2 mm but differ very significantly in the number of entire mesopores in
1 mm? in the intermacular—intermonticular areas, the number of entire acanthopores
in | mm? in the intermacular—intermonticular areas, and in the maximum apertural
diameter in mm of the zooecia in the intermacular—intermonticular areas.

Locality
Meaford Formation, Credit River, Streetsville, Ontario.

Type
Holotype ROM 12162; hypotypes ROM 12263, 12294 (unfigured).

Homotrypa streetsvillensis Dyer, 1925
Fig. 4A-B

Original Description (Dyer, 1925)

‘‘A ramose representative of the Homotrypa communis group is found in such numbers in a
definite horizon of the Streetsville member that it has been selected as the type fossil of the
zone.

‘‘In this species the branches vary from five to ten millimetres in diameter, and in some
cases reach a length of 50 mm. The surface is smooth without any indication of maculae; the
apertures indicate thick-walled zooecia of small but uniform size—twelve in two millimetres.

‘‘In tangential sections, the mesopores are few in number and the tubes polygonal in shape,
but as the axial region is approached the mesopores become numerous and the tubes become
rounded or oval in shape. Acanthopores of medium size are usually found at the angles of
junction of the walls. The characters of this species as revealed by vertical sections are very
much like those of Homotrypa communis, diaphragms being absent and the broken type of
cystiphragms, so characteristic of that species, being well shown.

‘The relationships of the present form, as already stated, are with H. communis, but a
decided difference from that species is indicated by the smaller size of the tubes and by the
absence of maculae of any kind. It perhaps resembles H. austini, Bassler, still more closely,
but differs in having the cystiphragms distributed evenly throughout the peripheral zone,
whereas in that species they are confined to the maculae.’’

Emended Description

Cotype ROM 12164 listed as Homotrypa streetsvillensis differs specifically from
cotypes ROM 12163 and ROM 12165 redescribed herein. ROM 12164 represents an
unidentified species known only from fragments, not necessarily related, but too
small to section. I consider it Homotrypa sp. indet. Cotype ROM 12165 is selected as
the lectotype and ROM 12163 as the paralectotype.

iS

EXTERNAL FEATURES

Zoaria ramose, dichotomous, round (with diameter 4 mm) to slightly compressed
branches (with minimum and maximum diameters ranging from 6 X 4, 11 xX 5, and
15 x 10 mm respectively); surface smooth but with small maculae flush with surface
and regularly spaced | to 1.5 mm apart measuring from centre to centre.

TANGENTIAL SECTION

Zooecia angular, apertures circular to oval, 10 to 12 zooecia in 2 mm in intermacular
areas (Table 4). Zooecial walls near surface thick, commonly 0.03 to 0.05 mm, but
up to 0.07 mm in maculae; composed of homogenous, concentrically arranged
laminae, with dark line of demarcation between zooecia commonly present. Meso-
pores few, indistinct (Table 4). Acanthopores abundant (Table 4), varying in diame-
ter from 0.02 mm (or less) to 0.06 mm, more numerous in maculae than in inter-
macular areas; each with small central lumen surrounded by dense, concentric
laminae. Apertural diameter of zooecia in mm in maculae 0.13 to 0.19 (Table 4), in
intermacular areas 0.07 to 0.13 (Table 4).

LONGITUDINAL SECTION

Zooecia curve gradually from outer axial region to periphery, opening slightly obli-
quely at zoarial surface. Zooecial walls thin in axial region, straight or locally
crenulated, thickening abruptly at base of peripheral area and maintaining that thick-
ness to surface, wall laminae broadly convex outwards, then sharply diverging at a
low angle before continuing into the diaphragms and cystiphragms and into the
diaphragms of the mesopores. Diaphragms in axial region of zooecia thin and widely
spaced, in certain sections absent (likely due to lack of preservation), one or two in
outer axial zone, and few sporadically developed near periphery. Cystiphragms
‘*hook-shaped’’, commonly one or two at base of peripheral zone where thickening
of the wall occurs, followed by one or two flat diaphragms spaced about one tube
diameter apart in outer half of zooecia. Acanthopores conspicuous mainly in
peripheral zone, with relatively large central lumen on either side of which laminae
diverge steeply, then pass into diaphragms and cystiphragms; acanthopores extend
beyond surface terminating into a pointed extremity, thus giving the surface a hirsute
appearance.

Remarks

Homotrypa streetsvillensis Dyer and Homotrypa communis Bassler are closely re-
lated. An examination of Bassler’s cotype USNM 41755 of H. communis shows the
presence of central clusters of mesopores in the maculae that are absent in Homotrypa
streetsvillensis. Measurements on Bassler’s type permit the quantitative comparison
of the two species. Table 4 shows that the two species differ significantly in the
number of mesopores in the intermacular areas, the number of acanthopores in the
intermacular areas, and the apertural diameter of the zooecia in the intermacular
areas.

Fig. 4 A-B. Homotrypa streetsvillensis Dyer, lectotype, ROM 12165.

A. Tangential section, x30.
B. Longitudinal section, x30.

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Locality
Meaford Formation, Upper Ordovician, Credit River, Streetsville, Ontario.

Type
Lectotype ROM 12165, paralectotype ROM 12163.

Homotrypella Ulrich, 1886
Homotrypella instabilis Ulrich, 1886.

Homotrypella hospitalis (Nicholson, 1881)
Fig. 5A-B

Monticulipora (Prasopora) selwynii, var. hospitalis Nicholson, 1881: 209.
Homotrypella expansa Dyer, 1925: 69.

Original Description (Dyer, 1925)

**A specimen was found in the Streetsville collection of Bryozoa in the Royal Ontario Museum
of Paleontology, which in its internal characters resembles Homotrypella hospitalis
(Nicholson), very closely. The growth, however, is vastly different from the typical growth of
the latter species, the zoarium being a broad, undulating expansion, 90 mm in diameter, with
an average thickness of three millimetres instead of a sub-hemispheric, sub-conical, or irregu-
lar compact mass. In places the expansion consists of a single layer, in other places of two or
more successive layers. Over the surface are evenly distributed low but distinct monticules,
which consist of tubes somewhat larger than average in size.

‘*The presence of monticules and the peculiar form suggest that the species might be referred
to the genus Monticulipora, but it has been retained in the genus Homotrypella on account of
its very close similarity, internally, to H. hospitalis, and because the walls are clear and
definite in structure. Bassler states that one of the best features for the determination of the
genus Monticulipora is the hazy, indefinite character of the walls.’’

Emended Description

EXTERNAL FEATURES

The zoarium described by Dyer as an ‘“‘undulating expansion’’ is a composite struc-
ture, made up of a number of nodular growths, individually varying in size from 15 to
40 mm wide and 12 to 20 mm thick, and the collective whole reaching 90 mm in
width. A polished surface in the longitudinal plane through one of the larger nodular
growths reveals a hitherto unsuspected alternating and progressively developing
stromatoporoid—bryozoan sequence starting on a mamelose stromatoporoid. Early in
the sequence is a growth 3 mm thick of Atactoporella densa Dyer (see description of
this species on p. 2). Homotrypella hospitalis (Nicholson) 11 mm in thickness
covers the entire assemblage except for a thin incrustation of Ceramoporella sp. too
poorly preserved to warrant description. Surface of specimen with inconspicuous
monticules | to 1.5 mm apart measuring centre to centre.

TANGENTIAL SECTION

Zooecia circular to subcircular, usually separated by mesopores 8 to 8.5 zooecia in
2 mm in intermonticular areas (Table 5); zooecial walls amalgamate. Acanthopores
relatively few to moderately numerous (Table 5), slightly inflecting, relatively large,
typically 0.02 to 0.06 mm in diameter but reaching 0.09 in monticules; consisting of
central lumen surrounded by dense, concentric laminae. Mesopores variable in size
and shape, relatively few to moderately abundant, angular to subangular (Table 5).
Monticules composed of zooecia and with thicker walls than in intermonticular areas;
maximum apertural diameter of zooecia in mm in monticular areas 0.23 to 0.32
(Table 5), maximum diameter of zooecia in mm in intermonticular areas 0.15 to 0.24
(lable 5):

LONGITUDINAL SECTION

Zooecia subprostrate for short distance, erect for most part, flaring slightly near
surface where section cuts summit of a lobe. Walls thin in axial region, thickening
slightly from subperipheral region to surface. Diaphragms throughout zoarium gener-
ally one-quarter to two tube diameters apart; some gaps in sequence attributable to
destruction through crystallization. Cystiphragms bulbous and overlapping, number-
ing at times 13 in | mm. Mesopores throughout section, with many close-set dia-
phragms. Acanthopores conspicuous, unusually well preserved particularly in
peripheral region; containing central lumen flanked by laminae diverging at low angle
from central tubule.

Table 5. Measurements of the taxonomic characters of Homotrypella hospitalis (ROM 254HR).

Measurements are given in millimetres. Figures in parentheses denote ranges.

n Mean’ "S.E.-

Number of zooecia in 2 mm in intermonticular area 20 8.2 = 0106
(8—8.5)

Number of entire mesopores in 1 mm? in intermonticular area 20 liG35e=2 (057
(8-21)

Number of entire acanthopores in 1 mm? in intermonticular area 20 14235 = 141
(8-28)

Maximum apertural diameter of zooecia in monticules 20 0.27 = 0.006

(0.23-0.32)

Maximum apertural diameter of zooecia in intermonticular area 20 0.18 + 0.005

(0.15—0.24)

Fig. 5 A-B. Homotrypella hospitalis Nicholson (H. expansa, Dyer),
hypotype, ROM 254HR.
A. Longitudinal section, x30.
B. Tangential section, 30.

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Remarks

Homotrypella expansa Dyer becomes a junior synonym of Homotrypella hospitalis
(Nicholson). Utgaard and Perry (1964) came to this conclusion although they did not
examine Dyer’s type. Measurements on the Whitewater types of Utgaard and Perry as
shown in their tables 11, 12, 13, 14, and 15 (1964; 64, 65) fall well within the range
of structural variation of Dyer’s type (Table 5).

Locality
Meaford Formation, Upper Ordovician, Credit River, Streetsville, Ontario.

Type
Hypotype ROM 254HrR.

Acknowledgments

Dr. Richard Boardman, Curator, Invertebrate Paleontology, of the United States
National Museum, kindly loaned relevant USNM types.

Thanks are expressed to Janet Waddington, Curatorial Assistant, Department of
Invertebrate Palaeontology, ROM, for calculating the Mann-Whitney U Statistics; to
John Monteith and Huibert Sabelis for the restoration of original thin sections and for
the preparation of new sections required for the research; to David Rudkin for assis-
tance with the figures; to Joan Burke for her valued assistance during the preparation
of the manuscript.

The photomicrographs were taken by Mr. Brian O’ Donovan, Department of Geol-
ogy, University of Toronto.

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oe

es

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23

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24

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