291 
S., 1, 1874, p. 18. Hall, 28th Ann. Rept. New York State Mus., 1879, p. 114. 
Ulrich, Jour. Cincinnati Soe. Nat. Hist., 5, 1882, pp. 154, 251. Foerste, Bull. 
Sci. Lab. Denison Univ., 2, 1887, p. 172. Hall and Simpson, Pal. New York, 
6, 1887, p. 15. Miller, N. A. Geol. Pal., 1889, p. 295. Ulrich, Geol. Surv. 
Illinois, 8, 1890, pp. 372, 416; Geol. Minnesota, 1893, 3, p. 275; Zittel’s 
Textb. Pal. (Engl. ed.), 1896, p. 275. Simpson, 14th Ann. Rept. State Geol. 
New York for 1894, 1897, p. 588. Nickles and Bassler, Bull. U. 8S. Geol. 
Surv., 173, 1900, pp. 36, 186. Grabau, Bull. Buffalo Nat. Sci., 7, 1901, p. 
167; Bull. New York State Mus., 9, 1901, p. 167. Cumings, 32d Ann. Rept. 
Dept. Geol. Nat. Res. Indiana, 1908, p. 741. Bassler, Bull. U. 8. Geol. Surv., 
292, 1906, pp. 40. Grabau and Shimer, N. A. Index Fossils, 1, 1907, p. 139. 
Henning, Archiy. fiir Zoél., 4, 1908, p. 48. Hallopora Bassler, Bull. U. S. 
Nat. Mus., 77, 1911, pp. 325-326; Zittel-Eastman Textb. Pal., 1913, p. 337. 
Zoaria ramose and bushy and often anastomosing. The zooecia are thin- 
walled in the immature region, and attain full development slowly. Dia- 
phragms are closely arranged in the tapering proximal portion of the zooe- 
cial tube, few or absent in the middle part, and few to numerous in the 
mature peripheral region. The apertures of the zooecia in the perfect state 
are closed by perforated ornamental covers which form diaphragms as the 
growth of the zooecial proceed. Acanthopores are absent. 
Hallopora spissata n. sp. Plate VIII, Figs. 1-2. Zoarium consists of irreg- 
ularly ramose, subcylindrical branches 5 to 10 mm. in diameter and from 1 
to 2 em. in length. The surface is smooth; maculae are absent. Zooecia 
are direct, angular, and thick-walled; 4 or 5 in 2 mm. Mesopores are en- 
tirely absent at the surface in completely matured specimens. 
In the tangential sections the zooecia are polygonal and in contact with 
each other on all sides. In sections of the surface of the submature zone or 
in tangential sections of immature specimens the zooecia are subcireular, 
separated at some of the angles by intercellular spaces (mesopores). Where 
the walls of adjacent zooecia are in contact the boundary between them is 
marked by a well defined dark line. 
The vertical sections show that few mesopores in which diaphragms are 
closely arranged are present at the bend from the immature to the mature 
region. They seldom reach the surface except in young specimens. In the 
axial region the narrow tapering zooecia which are scarcely wider than 
the mesopores are crowded with diaphragms. They are absent in the com- 
pletely developed zooecial tubes of the submature portion and in some of 
the zooecia of the mature zone. From one to three diaphragms usually are 
present near the bend of the immature and mature portions. The peripheral 
zone is narrow, varying from *4, to 1 mm. The walls thicken rapidly from 
the bend toward the surface, closing the mesopores and making the aper- 
tures subcircular. 
Hallopora spissata differs from H. splendens in having a narrower mature 
zone, less number of diaphragms in the submature and mature portions of 
the zooecial tubes and much thicker walls at the periphery of mature speci- 
mens. The less number of diaphragms, thicker walls and more direct 
apertures distinguish this species from H. ampla. 
