50 The Ohio Journal of Science [Vol. XXI, No. 2, 



Number of Arms. 



The absence of arms on all known Osgood forms referred 

 to Holocystites suggests that the latter were stiff and readily 

 broken off, as in the case of the arms of the very different genus 

 Comarocystites. The very distinct food-grooves are sufficient 

 evidence of arms on the protuberances at their ends, especially 

 in view of the fact that the food-grooves indent the margins of 

 these protuberances. 



There is no evidence of generic differences between species 

 having 5 arms and those having 4 arms. Among species with 

 4 rays there are both smooth forms with the quadrangular 

 margins surrounding the central oral aperture distinctly delim- 

 ited, and coarsely papillate forms with the corresponding quad- 

 rangular margins rendered more indistinct by the presence of the 

 papillae. Moreover, there are variations in the length of the 

 theca and in the arrangement of the plates which can not be 

 brought into co-ordination with any oral structure. 



ANAL APERTURE OF HOLOCYSTITES. 



One distinct advance in our knowledge of the anal aperture 

 has been made. This consists in the fact that the outline of the 

 anal aperture in all cases is polygonal, usually either pentagonal 

 or hexagonal, and covered with a pyramid consisting of as many 

 triangular plates as there are sides to the aperture. Many of 

 the specimens show the facets for the attachment of the plates 

 forming the pyramid, but the pyramid itself has been observed 

 in only one case, namely, in an undescribed species of Holo- 

 cystites, of the elongate type, as in //. alter?iatus, which is num- 

 bered 109G5 in Walker Museum of Chicago University, is labeled 

 as coming from Jefferson County, Indiana, probably is from the 

 Osgood formation, and retains distinctly 2 of the 5 plates 

 belonging to its anal pyramid. These plates are triangular, 

 almost equilateral in form, and are still in position. This 

 specimen had 4 arms. A study of the material accessible at 

 Chicago University led to the conclusion that no classification 

 could be based on differences in the number of plates forming 

 the anal pyramid. On the contrary, this number appeared to 

 vary from 5 to 6 in the same species in several cases. 



A study of the form of the theca and of the arrangement of 

 the plates of the theca also failed to show any generic differences 

 but led to other significant observations. 



