TREMATOPORID^E. 45 
occupy the space of 2 mm. The longer diameter of their aperture is about 0.20 mm., while 
the shorter or transverse diameter averages about 0.15 mm. The interstitial cells are 
numerous, usually completely isolating the true zoovcia. Their apertures vary in depth 
in different specimens, being in some not readily distinguishable from the true zocecial 
orifices and in others, on account of the interstitial membrane, scarcely detectable, being 
indicated only by shallow depressions between the peristomes of the true cells, which might 
be overlooked by a careless observer. Well-preserved examples show a number of small 
spiniform tubuli, whose position is usually on the peristomes. 
Tangential sections show that the true zocecia are elliptical in cross section, that their 
walls are slightly thickened by a secondary deposit on the inside, and that they are almost 
invariably completely isolated by a series of interstitial cells. These are angular, thin 
walled, and often larger than the true cells. A few spiniform tubuli may be detected, but 
not readily, on account of the many particles of pyrites of iron, which always obscure to a 
greater or less extent the minute internal characters of the bryozoa from the Waldron 
locality. 
Longitudinal sections show that the true zooecia are entirely without diaphragms. The 
peripheral region is very narrow, and, near the surface, always one and often two interstitial 
tubes separate the true zocecia. The interstitial tubes are usually crossed by but a single 
diaphragm, which is placed about midway between their point of origin and the apertural 
covering. The tube is generally a little restricted where the diaphragm occurs. 
This species differs from T . tuberculosa Hall in its much smaller, smooth, and cylindrical 
! branches, which have altogether a more delicate appearance. Compared with T. spiculata 
: Miller, it differs in its more elliptical and somewhat larger cell apertures and more distinct 
< peristome. 
Occurrence. — Quite abundant in the Waldron shales at Waldron and elsewhere in Indiana; 
less common in the Rochester shale at Lockport, N. Y., and Grimsby, Ontario. 
Catalogue numbers, 44108, 35763, U. S. National Museum. 
Trematopora spiculata Miller. 
PI. XXVII, figs. 14, 15. 
Trematopora spinulosa Hall, Twenty-eighth Ann. Rept. New York State Mus. (doc. ed.), 1876, pi. 11, 
figs. 11, 12. (Not T. spinulosa Hall, 1852.) 
Trematopora spiculata Miller, American Pal. Foss., 2d ed., 1877, p. 245. (Proposed for T. spinulosa, 
preoccupied by Hall in 1852.) 
Trematopora spiculata, Hall, Twenty-eighth Ann. Rept. New York State Mus. (Museum ed.), 1879, p. 
114, pi. 11, figs. 11, 12. 
Trematopora spiculata Hall, Eleventh Ann. Rept. Indiana Geol. Nat. Hist., 1882, p. 235, pi. 10, figs. 11, 12. 
The study of the type specimen of this species now preserved in the collections of the 
American Museum of Natural History showed that it is an example of a form occurring 
rather abundantly in the Waldron shale of Indiana and less commonly in the Rochester 
shale of New York and Canada. The identity of this species was not suspected hitherto, 
because, as the type specimen shows, the enlarged view of the surface figured by Hall incor- 
rectly represents this feature. The zocecia, instead of being angular and contiguous, as 
represented in this figure, are in reality subovate and separated by a row of angular meso- 
pores, which often attain a size equaling or exceeding the zooecia themselves. The follow- 
ng description is believed to set forth the salient features of the species. 
Zoarium of solid, ramose, frequently branching stems averaging 2 mm. in diameter. 
Zooecia oval to circular, with a more or less well-developed peristome, thin walled, 0.17 mm. 
md 0.14 mm. in their longer and shorter diameters, respectively, 7 in 2 mm., measuring 
engthwise. Interzooecial spaces often as wide as the zooecia and occupied by large, angu- 
lar mesopores. Acanthopores small, but often so numerously developed as to occupy 
wery angle, thus giving the spiculated surface. 
Compared with Trematopora whitfieldi Ulrich, the only closely related associated species, 
he present form may be distinguished by its more circular and smaller zocecia and rela- 
ively wider interapertural spaces. The acanthopores are also a more prominent surface 
eature and serve as an additional means of separating the two forms, 
