BRYOZOA. 563 



in the nodose character of the branches, but in its measure- 

 ments it is identical with young H. aspera. That it is only a 

 peculiar example of that species is shown by the facts, that on 

 other portions the nodes are on the dissepiments, and that the 

 superficial net-work is spinous. 



Position and locality: Keokuk group, Nauvoo, 111., Keokuk 

 and Beutonsport, Iowa. Not rare. 



HEMITRYPA ASPERA Ulrich. 



PL LVII, Pigs. 4-4f and 3a. 



Zoarium a flat, rapidly expanding, flabellate expansion, at- 

 taining a height of 3 or 4 cms., though usually not more than 

 2 or 3 cms. It grew upon some cylindrical. body over which it 

 spread to form a strong base. The example figured is stronger 

 in this respect than usual, but a good idea of this portion of 

 the zoarium can be gathered from it. The different sets of bars 

 forming the superficial net-work are indistinguishable near the 

 base, but farther up where the branches bifurcate less frequently, 

 we find that the principal bars are elevated, generally opposite 

 each second scala, into strong spines, that all the bars are thin 

 and approximately of the same thickness, and that the inter- 

 stices are rather irregular in shape and size,but, almost invaria- 

 bly, nineteen or twenty in 5 mm., measuring longitudinally. 



On the reverse near the base the branches and dissepiments 

 are rounded and thickened so as to be sub-equal and to make 

 the fenestrules sub-circular; their surface here is either smooth 

 or exhibits the remains of nodes. Farther up the fenestrules 

 are quadrangular, about 0.4 by 0.25 mm., and eight or nine in 

 5 mm.; the dissepiments half the width of the branches, some- 

 what depressed at the ends, but with the center elevated into a 

 prominent node. The branches are rigid, rounded and smooth, 

 and increase from 0.2 to 0.4 or 0.5 mm. before bifurcating; 

 about ten in 5 mm.; occasionally with a node that should have 

 been developed on a dissepiment. 



The nodes on the dissepiments and the strong spines on the 

 superficial net-work distinguish this species from all others. 



Position and locality: Keokuk group, Nauvoo, 111., Keokuk 

 and Bentonsport, Iowa. 



