BRYOZOA. 427 



ally well preserved specimens) minutely spinulose; but this is 

 never a conspicuous feature. Walls of zooecia thin, somewhat 

 flexuous in the axial region, slightly thickened in the peripheral 

 region. Apertures of zooecia circular from 0.15 to 0.20 mm. in 

 diameter, seven or eight in the space of two mm.; encircled by 

 a single series of large angular or subcircular mesopores, on an 

 average about two-thirds the size of the true zooecia. Diaphragms 

 rather few and remote in the zocecial tubes, in the mesopores 

 more numerous, and about their diameter or more apart. Acan- 

 thopores small, present in moderate numbers, and at times en- 

 croaching a little upon the zooecia. 



Aside from L. minutum (?) Rominger, the nearest congener of 

 this species is L.? wilmingtonense from Silurian strata. These 

 species have a facies rather different from the other species of 

 this genus, and should perhaps form a separate genus. In that 

 case L. subglobosum, and possibly L. wachsmuthi as well, will 

 go with them. 



Small examples of this species have been described by the 

 author as Callopora cincinnatiensis. The specimens were fur- 

 nished him by Mr. Fred Braun, who stated that he had col- 

 lected them from strata of the Cincinnati group, at Cincinnati, 

 0. This is now known to be an error, and careful comparison 

 with Iowa examples leaves no doubt as to their having been 

 collected at some western locality. 



Position and locality: Hamilton group. Occurs abundantly 

 at several localities in Iowa; (Independence, Rockford and Buf- 

 falo); also at Rock Island, 111. 



LEIOCLEMA MIXUTUM Rominger?. 



tFistxlipora minnta, Rominger, 1866. Proc. Acad. Nat. Sci. Phila. p. 120. 

 Callopora minntissima Nicholson, 1875. Rep't. Pal. Ontario, p. 77, fig. 43. 



This common species of the Hamilton group, closely resembles 

 the preceding in its minute structure, and it would be difficult to 

 point out any differences between them, excepting that of zoar- 

 ial habit. L. minuta, so far as observed, invariably occurs as 

 thin incrusting layers, a mm. or less in thickness, that by su- 

 perimposition of successive layers may eventually form small 

 masses. Such specimens are more common in the western lo- 

 calities than in Michigan and Canada. 



