NO. 1442. JAMES TYPES OF BRYOZOA-BASSLER. 13 



dome-shaped masses 400 mm. wide and 200 to 300 mm. in height. 

 The surface is generally monticulated, the monticules usually being 

 low and rounded but sometimes strong!}^ elevated and sharply pointed. 

 Nine of the ordinary zoa'cia may be counted in a distance of 2 mm. 

 Acanthopores are present in the successive mature zones, but are sel- 

 dom readily noticeable at the surface. 



The internal characters of this species are unusually well marked 

 and constant. A vertical section shows that the zoarium is made up 

 of successive zones distinguished by variations in tal)ulation and other 

 respects. Often the zones are separated by clay-tilled interspaces, 

 but in most cases the zooe.cial tubes are practically continuous through- 

 out a zoarium. In such specimens the individual zones can only be 

 distinguished by the alternate development of immature and mature 

 regions. In each of the successive immature regions the zooecia have 

 thin walls and few or no acanthopores. Diaphragms are present but 

 are separated from each other by distances varying from 1 to 2 

 tube diameters. This region passes upward, sometimes abruptly but 

 more commonly rather gradually, into the mature region in which the 

 walls are consideralily thickened, small acanthopores developed in 

 large numbers, and the diaphragms increased in number so that two or 

 even three occur in a distance equal to their own diameter. An occa- 

 sional curved or funnel-shaped diaphragm, like those frequentl}^ seen 

 in the typical species of the genus, also may be observed in the mature 

 region. Tangential sections passing through the mature zone bring 

 out especially the character separating the genus Amj)lexopora from 

 the otherwise quite similar group recentl}^ named Oyphotrypa. This 

 is, namely, the presence of a central black line separating the walls of 

 adjoining zooecia. In the latter genus the zooecial walls are so amal- 

 gamated that their boundaries can not be distinguished, the central 

 portion being clear or light colored. The zooecia in the immature 

 region have such thin walls that sections show no structural features. 



Occurrence. — Fairmount, Bellevue, and Corryville members of the 

 Covington group at man}" localities in the Ohio Basin. Cincinnati, 

 Ohio, is the type locality for both D'Orbigny's and James's specimens. 



AMPLEXOPORA PETASIFORMIS-WELCHI (James). 



MohticuUpora {Monotrypa) ■ivclchi James, Paleontologist, No. 6, 1882, ]>. 50; No. 7, 



1883, pi. I, figs. 4-4c. 

 Moniiculipura petcmformis var. welchi James and James, Jour. Cincinnati See. 



Nat. Hist., X, 1888, p. 169.— J. F. James, Jour. Cincinnati Soc. Nat. Hist., 



XVI, 1894, p. 187. 

 Amplexopora petasiformis-welchi Nickles and Basslkh, Bull. l^. S. Geol. Surv., 



No. 173, 1900, p. 165. 



This variety dii|ers from A. petaslformix only in the shape of the 

 zoarium, which tends to assume a subramose or ramose growth instead 

 of the usual hat-shaped masses. Variety welchi is of interest mainly 



