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



opposite side of the same specimen this arrangement in rows 

 may not be so evident. This arrangement is found in H. wykojffi 

 and H. sphceroidalis, with 5 arms, to which H. madisonensis 

 probably is closely related, with H. suhrotundatiis less certain. 

 This tendency toward the arrangement of the plates in trans- 

 verse rows is shown also by numerous ovate forms with coarsely 

 papillate surfaces, having 4 arms, and including H. afinis, H. 

 benedicti, H. ornatissimns, H. papulosus, and H. siibovatus. 

 Species of this type can not be differentiated generically from 

 the smoother ovate forms, with 4 arms, in which there is no 

 very obvious arrangement of the plates in transverse rows, as in 

 H. commodus, H. glohosus, H. gorbyi, H. hammelli, H. indianen- 

 sis, H. parvus, H. rotundatus, H. scitulus, and H. subglobosus. 



The studies here outlined have led to the conclusion that the 

 importance attributed to the types of species has given rise to 

 certain disadvantages as well as advantages. Although numer- 

 ous specimens of Holocystites were collected formerly in the 

 Osgood formation of southeastern Indiana, only the types were 

 highly valued and have gone into the important collections. 

 The other specimens became objects of trade and sale and have 

 become practically lost to science. Hence, from the meager rep- 

 resentatives of any one species it frequently is impossible to 

 determine the range of variation in form, arrangement of plates, 

 outline of oral or anal aperture, or the surface ornamentation. 

 While the writer is convinced that the species described by Miller 

 number only about one-fourth as many as indicated by the list 

 of names, the material for more exact discrimination is lacking. 



THE TERMS HOLOCYSTITES, MEGACYSTIS, AND 

 TREMATOCYSTIS. 



The generic name Trematocystis, proposed by Jaekel rests 

 on the Osgood species Holocystites subglobosus. This is one of 

 the smoother species with 4 arms, with a sharply angulate quad- 

 rangular border around the oral aperture, and with the plates 

 more or less arranged in transverse rows, but not conspicuously 

 elongated in a vertical direction along the lower of these rows. 

 As far as may be judged from our present knowledge of the 

 various Osgood forms, there is a considerable probability that 

 this term eventually must be discarded for either Holocystites 

 or Megacystis. 



