BRYOZOA. 597 



up. Beyond its influence the characters are as follows: Branches 

 strong, broadly convex, eight or nine in 1 cm. with an average 

 width of 0.8 mm., but increasing from about O.G mm. imme- 

 diately after bifurcation to about 1.1 mm. before again dividing. 

 Dissepiments short, slightly depressed, gradually decreasing in 

 width from the base toward the free margin, where their width 

 varies from 0.4 to 0.6 mm. Fenestrules comparatively small, 

 oval, increasing in width outward, with 6 or 6.5 in 1 cm. 

 Zooecia at first in four alternating ranges, then in five, six, and 

 seven rows (occasionally in eight) before the branch divides. 

 Apertures about twenty in 5 mm., small, circular, with faint 

 peristome, their diameter or more apart longitudinally, the 

 rows separated by a fine wavy line that is alternately stronger 

 and weaker and occasionally sufficiently elevated to form a 

 small node or spine. On the reverse the branches and dissepi- 

 ments are strongly rounded, upon the same plane, of nearly 

 equal thickness, and finely striated. The branches being thinner 

 than on the opposite face causes the fenestrules to be larger, 

 their average dimensions being about 0.8 by 0.6 mm. Their 

 form is somewhat variable, but, as a rule, they are broad-oval. 



The seemingly disproportionate strength of the zoarium, and 

 the striated solid tissue which is drawn over the basal portion 

 of both sides, give this species a decidedly distinct appearance. 

 In many respects the species resembles P. complanata, but that 

 form is larger, more regular, has the zooecia open down to the 

 foot-stalk, the branches less convex and more uniform, the 

 feuestrules smaller and circular, and no striations between the 

 zooecia apertures. 



Position and locality: Chester group, Chester, 111. 



POLYPORA COMPLANATA UMch. 

 PL LX, Fig. 6-6c. 



The above name is proposed for the specimen figured and one 

 other. A number of fragments now before me may represent 

 young examples of the same species but as their general appear- 

 ance is more like that of P. corticosa. and, as none of them 

 expand as rapidly as the types, I prefer to leave them unclassi- 

 fied for the present. The types which expose only the obverse 

 side may be described as follows: Zoarium a semi-circular and 



