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Life Sciences
Occasional Papers

Royal Ontario Museum
June 30, 1971

No. 18

The Trepostomatous Bryozoan
Stigmatella catenulata diversa Parks and Dyer
(1922), a synonym for Mesotrypa diversa
(Parks and Dyer)

by Madeleine A. Fritz1

Among the specimens of the genus Stigma-
tella Ulrich and Bassler (1904) contained
in the type collection of the Department of
Invertebrate Palaeontology of the Royal
Ontario Museum is one labelled Stigmatella
catenulata diversa Parks and Dyer (1922).
In my current study of the types of Stigma-
tella established by the above authors I have
questioned the validity of the generic refer-
ence of this particular taxon. In order to
substantiate this belief, technical work on
the specimen was necessary. Broken frag-
ments were pieced together to determine the
shape of the zoarium; the original thin sec-
tions, which had deteriorated, were re-
mounted, and one new section was prepared.
After a study of the material it was evident
that the species belonged to the genus Meso-
trypa. A redescription of the specimen forms
the subject of this paper.

Order TREPOSTOMATA Ulrich 1895

Family MONTICULIPORIDAE

Nicholson 1881 (emended Ulrich 1895)

Genus Mesotrypa Ulrich 1895

Type species — Diplotrypa infida Ulrich 1 886.

Mesotrypa diversa (Parks and Dyer, 1922)

(Fig. 1, A-D;Fig. 2, A,B)
1922 Stigmatella catenulata diversa Parks
and Dyer, p. 14, pi. m, figs. 8, 8a.

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Original description — "The main portion of
the zoarium of this variety is a roughly
spindle-shaped mass about 40 mm long and
20 mm wide at the middle. From this cen-
tral mass a few branches seem to have been
given off but as they are broken away nothing
can be said as to their length. The surface is
covered with large rounded monticules at
intervals of about five millimetres. The aper-
tures of the zooecia between the monticules
are fine and regular but on the summits a
great diversity in size is to be observed.

"Vertical sections . . . [show] . . . more
numerous diaphragms [compared with two
varieties of Stigmatella catenulata (Turnings
and Galloway, 1913] . . . Mesopores few,
except in restricted areas, not well developed
in the mature region; zooecial walls crenu-
lated and passing into the chain-like meso-
pores in the immature region.

"Tangential sections . . . very distinctive.
The general field shows regular, polygonal,
thin-walled zooecia to an average number of
ten or eleven in the space of two millimetres.
In this region mesopores are very few and
small. Acanthopores are well developed,
usually, but not always, at the angles of
junction of the zooecial walls and sometimes
slightly inflecting the tubes. At intervals of
about five millimetres the structure is dis-
tinctly different as the zooecial tubes are

1. Research Associate, Department of Invertebrate Palaeontology, Royal Ontario Museum, Toronto.

large and rounded, the mesopores numerous
and of very irregular shape, and acantho-
pores practically absent.

"Externally this variety can easily be
recognized by the large rounded monticules;
in tangential section the structure as de-
scribed above is unique; . . ."

Emended description —

External features — A single specimen (Fig.
1, B,C), tapering at base but showing no
sign of attachment, expanding to an inverted
cone, linear dimension about 30 mm, maxi-
mum diameter 15 mm; from side of cone
and from summit arise round to slightly
flattened branches (six in all), base width
five to ten mm, only bases preserved. Sur-
face with conspicuous bun-like monticules
3.5 mm in diameter, raised 0.5 to 1 mm in
height, distance from centre to centre gen-
erally 5 mm. Surface with protruding blunt
acanthopores.

Tangential section — Zooecia angular, sub-
angular to subcircular in intermonticular
areas. Zooecial walls mostly 0.03 to 0.04
mm thick, rarely 0.05 mm. Wall concentri-
cally laminated. Mesopores small and of
various shapes. Acanthopores in places
slightly inflecting, located at the juncture of
zooecia, (Fig. 1, D; Fig. 2, A) eight to nine
may occur where four zooecia are in contact,
six to seven where three meet; diameter
usually 0.02 to 0.03 mm, few 0.06 mm,
central lumen surrounded by concentrically
laminated tissue. Monticules with larger
zooecia than in intermonticular space, com-
monly circular, and with more numerous
mesopores, latter occasionally in small clus-
ters of relatively large and small tubes (Fig.
1,A).

Longitudinal section — Zooecia at base briefly
subprostrate, then broadly curved, finally
straightening to intersect zooecial surface at
right angles. Walls thin in axial zone, thick-
ening slightly toward surface, finely crenu-
lated throughout and laminated, laminae
diverge at low angle and pass into the
diaphragms. Acanthopores present through-
out but petering out at various intervals, the
last generation protrude bluntly at the sur-
face; each with a clear central area from
which laminae diverge at a low angle and

pass into diaphragms when the two struc-
tures are in juxtaposition. Mesopores with
close-set diaphragms, chain-like owing to
constriction in walls where diaphragms and
wall meet (Fig. 2, B); more numerous in
deep sections than at surface. Diaphragms in
zooecia relatively numerous; horizontal,
oblique, curved to cystoid, six to seven in
1 mm, about one-half to two tube diameters
apart.

Remarks — Mesotrypa diversa may be dis-
tinguished externally by the shape of the
zoarium, by the conspicuous monticules, and
by the protruding blunt acanthopores.
M.pauca Utgaard and Perry (1964), the
most closely related species, from a Rich-
mond horizon resembles M. diversa in hav-
ing few mesopores. M. diversa, however, is
distinguished from M. pauca in having still
fewer mesopores (Table i), fewer and
smaller acanthopores which seldom inflect,
finely crenulated zooecial walls, and fewer
diaphragms.

Occurrence — Dundas Formation, Humber
Member, Humber River, Upper Ordovician,
Weston, Ontario.

Type — Holotype, Department of Inverte-
brate Palaeontology, Royal Ontario Museum,
Toronto, ROM 1089H.R.

Holotype (2G128) and Paratype (2G129)
of M.pauca are housed in the paleologic
collection of the Indiana Geological Survey,
Bloomington, Indiana.

Acknowledgments — Thanks are expressed
to Mr. John Monteith, Department of In-
vertebrate Palaeontology, for the expert
restoration of the specimen and for the
skilful preparation of the thin sections, to
Mr. L. Kisko, Department of Zoology, Uni-
versity of Toronto for his generous assistance
with the statistical analyses, and to Miss
Joan Burke for her careful typing of the
manuscript.

I am indebted to Professor T. G. Perry,
Department of Geology, Indiana University,
Bloomington, Indiana, and to Dr. T. E
Bolton, Geological Survey of Canada, Ot-
tawa, for their appraisal of this paper.

The photomicrographs were taken by Mr.
B. O'Donovan, Department of Geology,
University of Toronto.

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Figure 1

Mesotrypa diversa (Parks and Dyer), Holotype

(ROM 1089H.R.)

A. Tangential section, showing in particular
three monticules, X 15.

B. Portion of surface, X 4.

C. Entire specimen, X 2.

D. Tangential section, X 30.

Figure 2

Mesotrypa diversa (Parks and Dyer), Holotype

(ROM 1089H.R.)

A. Tangential section, X 60.

B. Longitudinal section, X 30.

Literature Cited

Cumings, Edgar R. and Jesse J. Galloway

1913 The stratigraphy and paleontology of the Tanner's Creek section of the Cincinnati
Series of Indiana. 37th A. Rep. Indiana Dep. Geol. and Nat. Resour., pp. 353-479.
Nicholson, Henry A.

1881 On the structure and affinities of the genus Monticulipora and its subgenera with
critical descriptions of illustrated species. Edinburgh, W. Blackwood. 240 pp.
Parks, William A. and W. S. Dyer.

1922 The stratigraphy and paleontology of Toronto and vicinity, pt. n — the Molluscoidea.
A. Rep. Out. Dept. of Mines, vol. 30, pt. 7, pp. 1-43.
Simpson, George G., Ann Roe and Richard C. Lewontin.

1960 Quantitative Zoology. Revised edition. New York, Harcourt, Brace. 440 pp.
Ulrich, Edward O.

1886 Report of the Lower Silurian Bryozoa with preliminary descriptions of some new

species. Extracted from 14th A. Rep. Minn. Geol. Nat. Hist. Surv., pp. 58-113.
1895 On the Lower Silurian Bryozoa of Minnesota. Minn. Geol. Nat. Hist. Surv., Final
Rep., vol. 3, pt. 1, pp. 96-332.
Ulrich, Edward O. and R. S. Bassler

1904 A revision of the Paleozoic Bryozoa, Pt. n On the genera and species of Treposto-
mata. Smithsonian Misc. Collns., vol. 47, pp. 15-55.
Utgaard, John and T. G. Perry

1964 Trepostomatous Bryozoan fauna of the upper part of the Whitewater Formation
(Cincinnatian) of eastern Indiana and western Ohio; Bull. Indiana Dept. of Con-
servation, Geol. Surv., 33, 1 11 pp.

Suggested citation: Life Sci. Occ. Pap., R. Ont. Mus.

All manuscripts considered for publication are subject to the scrutiny and editorial policies of the Life
Sciences F.ditorial Board and to review by persons outside the Museum staff who are authorities in the
particular field involved.

price: 50<f

© The Royal Ontario Museum, 1970

100 Queen's Park, Toronto 181, Canada

PRINTED AT THE UNIVERSITY OE TORONTO PRESS

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