26 McMURRICH 



mesenteries and ending somewhat abruptly at either edge. At 

 the outer edge a mesogloeal process, stronger than usual, is 

 developed and from it a number of mesogloeal processes arise. 

 The parieto-basilar muscles form a distinct fold on the lower 

 portions of the mesenteries, and the basilar is fairly well devel- 

 oped, having the appearance shown in PI. Ill, Fig. 20. 



Both the inner and outer mesenterial stomata are present, 

 and all the mesenteries, with the exception of those of the 

 fourth cycle and the directives, bear reproductive organs. 



From the examination of this species it has seemed to me 

 impossible to separate it from the genus Cribrina. Verrill ('69) 

 has established for its reception the genus Evactis characterized 

 b}' possessing pores in the column wall as well as verrucae and 

 bv the tentacles beino- ectacmaeous. I have not been able in 

 sections to discover any distinct pores in the column wall and 

 am inclined to believe that the emission of jets of water " as 

 from a watering pot " which has been observed, was through 

 minute ruptures of the wall, the mesoglcea being comparatively 

 thin especially in the upper part of the column. If this be 

 correct, little importance can be attributed to their power of 

 ejecting water. The tentacles of C. arteinisia are, indeed, 

 ectacmseous but in every other respect the form has the typical 

 structural characteristics of a Cribrina, and it seems advisable 

 to regard the ectacmaeous arrangement of the tentacles as a 

 specific rather than as a generic peculiarity. 



Genus Urticixa Ehrenberg. 



Cribrinidae without true acrorhagi ; with numerous perfect 

 mesenteries frequently arranged decamerously ; sphincter 

 strong ; ectodermal musculature of the disk and tentacles im- 

 bedded in the mesogloea ; column wall destitute oi an epider- 

 mal covering, and usually provided with verrucae arranged 

 more or less definitely in vertical series ; tentacles simple. 



The synonymy of this genus has been recorded by Andres 

 ('83) and more recently by Carlgren ('93). As at present un- 

 derstood it includes but a single species, A. crassiconiis, a fact 



