46 BRYOZOAN FAUNA OF THE ROCHESTER SHALE. 
Occurrence. — Rather uncommon both in the Waldron shale at Waldron, Ind., and in the 
Rochester shale at Lockport, N. Y., and Grimsby, Ontario. Rare in the Osgood beds at 
Osgood, Ind. 
Catalogue numbers, 35760, 35762, U. S. National Museum. 
MONOTRYPA Nicholson. 
The massive zoarium consisting of simple, large, prismatic zocecia, with thin, straight, 
or crinkled walls, usually few diaphragms, and no acanthopores or mesopores, is character! 
istic of this genus. The species described below represent two sections of the genus, one 
in which the zocecia have crinkled walls and no diaphragms and the other with straight 
walls and diaphragms. However, as various species are intermediate in their character! 
between these extremes, this division of the genus is probably more an artificial than a 
natural one. 
MONOTRYPA OSGOODENSIS n. sp. 
PI. XVI, figs. 1-5. 
Compare A strocerium constrict um Hall, Nat. Hist. New York, Pal. [1, 1852, p. 123, pi. 34A, figs. 2a-c, 3a-3 
Zoarium massive, generally consisting of flat or hemispherical disks lOto 20 mm. in diam- 
eter and 4 to 10 mm. high, but sometimes of larger rounded masses 20 to 30 mm. in thick- 
ness. Growth commences upon other organisms, but as it continues the zoarium becomes 
free and the base lined with a concentrically wrinkled epitheca. Cellulil'erous surface 
smooth, the zocecia composing the maculae being a trifle larger than the ordinary ones and 
on a plane with them. Zocecial apertures thin walled, polygonal in outline, usually hex- 
agonal, A to 5 in 2 mm. Acanthopores and mesopores wanting, the structures simulating 
the latter probably being young zocecia. 
•Sections show thai the walls are thin and straight , that the diaphragms are developed at 
intervals of from a tube diameter or more apart in the immature region to three in the same 
space in the mature zone. The immature and mature regions are very similar, hut may 
be distinguished by the more numerous diaphragms and slight thickening of (he walls in 
the latter region. Large zoaria often show successive immature and mature regions. 
Specimens of this species are very similar externally to the associated M. benjamirm 
but a vertical fracture will show the differences, M. osgoodensis having straight walls and 
diaphragms and M. benjamini showing crinkled walls, no diaphragms, and slightly larger 
zocecia. The zocecia of Orbignyella rxpanm are also quite similar in size and shape, but 
the explanate growth and different internal structure will distinguish it. Hall has proh- 
ably included this species with, his Astrocerium constrictum, as some of his figures of the 
coral appear to represent this bryozoan.. There should be no difficulty in separating the 
t\\<>, hecause of the thick walls and projecting septa of the coral. 
Occurrence. — Abundant in the Osgood beds at Osgood, Ind., not uncommon in the Koch-. 
estei shale at Lockport and Rochester, N. Y. 
Catalogue numbers, 35498, 35499, 44118, U. S. National Museum. 
MONOTRYPA BENJAMINI II. sp. 
PI. XVI, figs, fi-9; PI. XXVI, fig. 11. 
Zoarium of globular or subglobular masses a centimeter or more in diameter. Surface 
smooth, macula^ not conspicuous. Zocecia angular, thin walled, usually 4 in 2 mm.; dia- 
phragms wanting. Zocecial walls finely erenulated, 15 or more wrinkles in 2 mm. 
This species is congeneric and, indeed, very closely related to the genotype of Hall's genus 
Ptychonema, P. tabulatvs from the Lower Devonian of New York. Judging from the 
description and figures, Hall's species forms larger zoaria, has slightly larger zocecia, and 
more widely separated corrugations than the form here described. The genus Ptychonema 
was established for species having slightly corrugated walls and no diaphragms. As the 
genotype of Monotrypa has crinkled walls and few diaphragms and other species of the 
