201 



S., 1, 1874, ]). V.\. Hall, IJSlli Ann. i:c|>t. New Ycuk Stal.- Miis.. l.S7f>. p. 114. 

 Ulric'h, Jour. ("iiK-inimti Soc. Nal. Ilisl., .",. issij. pp. i.-,l, i:r,l. iM.cistc r.nll. 

 Sci. Lab. Donlsoii Univ., 2, 1887. i.. t7J. Hall and Sinipsdii. I'al. New V<iik. 

 C. 1887. p. ir.. Miller. \. A. (W'ol. Pal.. 1889, p. 29.j. Ulricli, Geol. Surv. 

 lUinoi.s, 8. 1S!M>. pp. .•;7l'. 41(i : (icM.l. Minnesota, 1893, 3, p. 275; Zittel'.s 

 Toxtl). Pal. (Kufil. (>(].), 189(5, p. 27"). Simpson, 14tla Ami. Kept. State Geol. 

 Xew York for 1894. 1897, p. 588. Nickles and Bassler, liull. V. S. (ieol. 

 Surv., 17:{. liKIO. pp. :{(;, 18(5. Grabau. P.nll. Buffalo Nat. Sei., 7, IfK)!, p. 

 1(57: Bull. Xew York State Mus., 9, lfM)l. p. 1(57. Cumin^s, :i2d Ann. Kept. 

 Dept. (Jeol. Nat. Kes. Indiana. 1908. p. 741. Bas.sler, Bull. V. S. Geol. Surv., 

 292. 190(5. i)p. 40. Crahau and Shinier, N. A. Index Fossils. 1, 1907, \k 139. 

 Hennins. Arehiv. fiir Zor.l., 4. 1908. p. 48. Hallopora Bassl(>r, Bull. U. S. 

 Nat. Mus„ 77, 1911, pp. 325-32(5; Zittel-Eastman Textb. Pal., 1913, p. 337. 



Zoaria ramose and bushy and often anastomosing. The zooecia are tliin- 

 walled in the immature rejiion, and attain full development slowly. Dia- 

 phragms are closely arranjied in the tapering proximal porti<m of the zooe- 

 cial tube, few or absent in the middle part, and few to numerous in tlie 

 mature peripheral region. The apertures of the zooeeia in the perfect state 

 are elosed by perforated ornamental covers which form diaphi'agms as the 

 growth of the zooecial proceed. AcanthoiK)res are absent. 



Hallopora spissata h. sp. Plate VIII, Figs. 1-2. Zoarium consists of irreg- 

 idarly ramose, snbcylindrical branches 5 to 10 mm. in diameter and from 1 

 to 2 cm. in length. The surface is smooth ; maculae are absent. Zooecia 

 are direct, angular, and thick-walled : 4 or 5 in 2 mm. Mesoixires are en- 

 tirely absent at the surface in compleli'ly 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 subcircular, 

 separated at some of the angles by intercellular spaces (mesopores). "Where 

 the walls of adjacent zooecia are in contact tlie boiuidary between them is 

 marked by a well defined dark line. 



Tlie vertical .sections show that few mesopores in which diaphragms are 

 clo.<;ely arranged are present at the bend from the immature to the mature 

 regicm. 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 (»f the submature portion and in some of 

 the zooecia of the mature zone. l<"rom one to three diaphragms usually are 

 present near the bend of the immature and mature portions. The i)eripheral 

 zone is narrow, varying from ='1 to 1 mm. The walls thicken rapidly from 

 the bend toward the surface, closing the mesojiores and making the aper- 

 tures subcircular. 



Hallopora npist^ata differs from //. .splciidc^s in having a narrower mature 

 Z(me. 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 diapliragms, thicker walls and more direct 

 apertures distinguish this species from //. ampla. 



