﻿ulrich-bassler] revision of paleozoic bryozoa 31 



in diameter. Zooecia thin-walled, 9 to to in 2 mm. Acanthopore 

 few, small but well marked. \n immature regions diaphragms from 

 one to one and a half times their own diameter apart ; in the mature 

 regions two or three times as numerous. 



The small, usually subglobose, zoarium, few acanthopores and the 

 tabulation characterize this species. An externally very similar spe- 

 cies of Cyphotrypa occurs in the Richmond formation of < >hio. 



Occurrence. — Trenton of Iowa, Minnesota, Kentucky, and 

 Canada. 



Cat. Nos. 43,189-43,191, U. S. X. M. 



CYPHOTRYPA WILMINGTONENSIS new species 



I I'l ATE VIII, 4-6) 



Zoarium of small, smooth, rounded or subglobular masses about 10 

 mm. in diameter. Zocecia thin-walled, angular, and when well pre- 

 served exhibiting strong acanthopores at the junction angles. 

 Zocecia of the maculae but slightly larger than the ordinary, 7 to <S 

 of the latter in 2 mm. Thin sections show that the acanthopores 

 are large and distinct, with a well-marked central perforation, and 

 usually occupy only the angles formed by adjoining zocecia. Dia- 

 phragms twice their own diameter or more apart in the immature 

 region and two to three times as numerous in the mature. 



The size of the zocecia, numerous large acanthopores, and small 

 globular method of growth distinguish this species from most others 

 of the genus. It has much larger acanthopores than C. acervulosa. 



Occurrence. — In shaly limestone of Richmond age at Wilmington, 

 Illinois. 



Cat. No. 43.192, U. S. N. M. 



Genus Atactopora Ulrich 



Until recently this genus has been classed with the Amplexo- 

 porida, but since we have come to appreciate the importance of 

 differences in the minute structure of the zocecial walls, we can s< e 

 that it is more naturally placed with the Heterotrypidcz. The wall 

 structure is precisely as in Heterotry pa, the light-colored line or band 

 being present between adjoining zocecia. The incrusting zoaria, 

 with the subsolid elevated maculae and the numerous small acantho- 

 pores inflecting the zocecia, characterize the genus. Two species 

 have been described, A. hirsuta the genotype and A. maculata. Sev- 

 eral new forms are known, the following, though a good Atactopora, 

 having fewer acanthopores than usual. 



