TREMATOPORID.E. 43 
Zooecia larger than is usual in species of this genus, with subangular apertures and mod- 
erately thin walls, an average of 4 in 2 mm. Mesopores usually small and comparatively 
few at the surface, larger and more abundant at deeper zones in the zoarium. Opercula 
closing the zooecia not observed at the surface, but detected in tangential sections. 
Internal characters. — Tangential sections exhibit considerable variation in the size and 
shape of the zooecia and the size and number of the mesopores. The reason for this is 
seen in vertical sections. Commencing with the mature region, mere or less numerous 
mesopores are developed and these, as the surface of the zoarium is approached, are seen 
to, become gradually smaller and less numerous and often pinched out altogether at the 
surface, the zocecial diameter consequently becoming greater. A tangential section there- 
fore passing through the early part of the peripheral region will show numerous mesopores 
and rounded 'zooecia, while one taken just below the surface of the zoarium exhibits few 
and small mesopores and larger, angular zooecia. In each case, however, because of this 
relation between the zooecia and mesopores, the number of zooecia in a given space is the 
same, even though they vary in diameter. 
The surest guide for the identification of C. magnopora is the vertical section where the 
tabulation of the tubes is exhibited. All of the many specimens and sections examined 
indicate that the tabulation is the most constant feature of this as well as all the other 
species of the genus. The zooecial tubes are closely tabulated at their inception, this tab- 
ulation continuing until the normal diameter of the zooecia has been reached. Then 
diaphragms are absent altogether until the peripheral region is reached, and here they are 
uncommon, only one or rarely two being inserted m each tube. 
The large zoarium and the peculiar tabulation of C. magnopora is so different from other 
species of the genus that comparisons are scarcely necessary. Vertical fractures when 
moistened and examined under a lens show the characteristic tabulation so well that sec- 
tions are not a necessary adjunct for the identification of the species. The identification 
of the species in the Rochester shale is based upon a single example from Grimsby, Ontario. 
This specimen is a well-preserved subcylindrical branch 35 mm. in length and 10 mm. in 
diameter. The external characters are the same as in the typical Clinton specimens and, 
as our figures here given will show, the internal features of the two are identical. 
Occurrence. — Abundant in the Clinton formation at Dayton, Centerville, and other local- 
ities in Ohio. Rare in the Rochester shale at Grimsby, Ontario. 
Catalogue numbers, 35532, 44131, U. S. National Museum. 
Family TREMATOPORIDiE TTlricH. 
Genus TREMATOPORA Hall. 
Ulrich has shown in his "American Paleozoic JBryozoa" that of the numerous species 
referred to this genus by Hall only a few are congeneric with the common Rochester shale 
form, T . tuberculosa, the first species following the generic definition. The genus and 
species have been well defined by Ulrich in the work cited above, and the following descrip- 
tion is but an adaptation from this author, the numerous specimens and thin sections 
showing no additional features. 
Tremalopora has many characters in common with the prolific Ordovician genus Batostoma 
and is probably the Silurian representative of the latter. The general internal structure of 
the two genera is similar, but the few diaphragms in the zooecia, beaded mesopores, rounded 
zooecia with more or less well-developed peristomes and comparatively small acanthopores, 
and the solid interspaces are characteristic of Trematopora. 
Trematopora tuberculosa Hall. 
PI. XIII, figs. 15, 16; PI. XV11, fig. 1-3; PI. XXV, fig. 8. 
Trematopora tuberculosa Hall, Nat. Hist. New Vork, Pal. II, 1852, p. 149, pi. 40A, figs. lag. 
Trematopora tuberculosa Ulrich, Jour. Cincinnati Soc. Nat. Hist., VI, 1883, p. 259, pi. 13, figs. 2-2b. 
Trematopora tuberculosa Grabau, Bull. New York State Mus., No. 45, 1901, p. 166, fig. 65. 
Zoarium of irregularly ramose, solid, often flattened branches, an average specimen 
being 5 or G mm. wide and 3 or 4 mm. in thickness. Surface studded usually with low 
Bull. 292—06 4 
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