30 BRYOZOAN FAUNA OF THE ROCHESTER SHALE. 
As is usual with species of this genus, the zocecial apertures vary considerably in appear- 
ance at the surface. In young stages the apertures are elongate, the walls slightly raised 
posteriorly and often confluent with those of the next zocecium, thereby giving a striate 
appearance to the branch. With age the apertures become more direct and v polygonal, 
the walls ridge-shaped and thickened, and numerous blunt acanthopores appear. In the 
latter condition a few mesopores are observed, these/usually appearing as shallow depres- 
sions between the zocecia. Measuring longitudinally, 4 zocecia may be counted in 2 mm. 
Thin sections bring out especially the large number of acanthopores and the thick 
zocecial walls characteristic of the species. They also show that the tabulation is very 
much like that prevailing in the typical Ordovician species of the genus, namely, that 
diaphragms are most abundant near the turn from the axial to the peripheral region, that 
they are present hut less numerous in the axial region, and that they are often wanting in 
the outer part of the peripheral zone. The acanthopores are very large for the genus and 
are most frequently arranged in rows paralleling the length of the branch- Sometimes as 
many as fourteen are seen surrounding a zocecium, although eight is the usual number] 
The mesopores are irregularly developed an 1 are of various sizes and shapes. When seen 
in vertical sections they show the usual development of diaphragms. Comparisons with 
the associated and somewhat similar species E. striata (Hall) are given under the description 
of that form. 
Occurrence. — Not uncommon in the Rochester shale at Grimsby, Ontario, rare at 
Lockport and Lewiston, hut more abundant at Rochester, N. Y. Common in the Osgood 
beds at Osgood, lnd. 
Catalogue numbers, 35521, 35522, 35739, 4412S, U S. National Museum. 
Eridotrypa noddlos 
\ n 
. sp. 
PI. XI. figs n, 15; I'l XXV figs. 1 3. 
Zoarium of small, slender, cylindrical, monticulated branches about 2 mm. in diameter, 
dividing at intervals of 10 nun or more. The maculae are developed sometimes as sharp 
tubercules, but usually as strongly elevated elongate monticules which by their confluence 
assume an annular or spiral arrangement. Zocecia varying, according to the maturity of 
the specimen, from oval oblique in young examples to polygonal in older specimens. A 
lew small acanthopores are sometimes observed at the surface and mature examples show 
mesopores to be present. 
Internal characters P>ecause of the very short peripheral region, tangential sections are 
difficult to prepare but sections of a very old example show polygonal zocecia, large and 
irregular mesopores and small acanthopores. Diaphragms wanting in both zocecia aril 
mesopores. 
The strongly monticulated zoarium distinguishes this from small ramose forms associated 
with it. Trematopora luberculosa has a similar monticulated zoarium, but its branches are 
considerably larger and the external and internal features are totally different, as a glance 
at the figures will show 
Occurrence.— Not uncommon at Lockport and Rochester, N. Y. 
Catalogue number, 35524. U. S .National Museum. 
Eridotrypa solida (Hall). 
PI. XII, figs. 7-9, PI. X XI V. tigs. 20-23; PI. XXV, fig. 16. 
Trematopora solida Hall, Nat. Hist. New York, Pal. 1 1 1852, p. 15.3, pi. 40A, tips. 6a e. 
Homotrypa f solida Nickles and Bassler, Bull. U. S. Geoi. Survey No. 173 ; 1900, p. 293. 
This is one of the largest solid, ramose bryozoa occurring in the Rochester, and th< 
thick cylindrical branches varying from 5 to 10 mm. in diameter, together with the smootl 
surface, thin-wallcd angular zocecia, and few mesopores, distinguish it from the associate< 
forms. 
