DESCBIPTI0N8 OF THE SPECIES. 22] 



folds on each side of an ambulacrum. Spiracles small, appearing as linear slits 

 between the Lancet-plate and the deltoid ridges, which are of variable width. The 



posterior pair may open separately at the sides of the amis, beneath a kind of hood 

 formed by the deltoid plate, or be confluent with it, so as to form one large anal 

 spiracle. Surface usually much ornamented with granular striae. Column circular. 



History, The species which we have taken as the type of this genus was described 

 by Shumard l by the name of Pentremites Sayi, though he stated that it " presents all 

 the essential characters of the genus Ehmcrinus, Roemer." In this respect he was 

 perfectly correct, for the presence of an anal plate in the posterior interradius of 

 Elasacrinus had not then been discovered. Later on, however, the species was 

 referred to both by Shumard and by Messrs. Meek and Worthen as Granatocrinus 

 Sayi, and it has been generally known by this name in America. For all Blastoids 

 (except Elceacrinus) with linear ambulacra extending along the whole length of a 

 globose or ovoid calyx were referred to this genus, whether they had five spiracles 

 piercing the deltoids or ten " excavated, one into each lateral margin of these 

 pieces " 2 . 



This important difference had not, however, escaped the notice of Messrs. Meek 

 and Worthen, though they never gave a definite expression to their views by pro- 

 posing a new generic name. This step was taken by ourselves in 1882, when we 

 took Pentremites Sayi, Shumard, as the type of a new genus Schizoblastus, and we 

 referred to it all the American species of Granatocrinus which have the spiracles in 

 pairs at the sides of the deltoid plates, and not piercing their central ends. 



Further investigation, however, has led us to separate off two of these under the 

 generic name Cryptoblastus, while two others will probably fall into the new genera 

 Mesoblastus and Ileteroblastas, which we have established for certain British 

 Blastoids. This has rendered us very uncertain as to the generic position of species 

 which we have not personally examined ; and the only American species which we 

 can definitely refer to Schizoblastus, in addition to Pentremites Sayi, Shumard, is the 

 Granatocrinus melonoides of Meek and Worthen. On the other hand we must now 

 transfer to Scltizoblastus an Irish species which we formerly referred with doubt to 

 Granatocrinus (G. Bofei), and we can further add a fourth species also from Ireland 

 (S. Bailii). 



Remarks. The calyx of Schizoblastus is either subglobose as in 8. Sayi and S. 

 Bailii (PI. XVI. fig. 13), and in a less degree in S. Bofei (PI. VIII. fig. 10), or more 

 elongated and melon-shaped as in S. melonoides (PI. VI. fig. 15). In the first- 

 named species the section is fairly pentagonal, but in the other three it is rather 

 more decagonal (PI. VI. figs. 16, 17; PI. VIII. fig. 9; PI. XVI. fig. 12). The 



1 ' Pakcontological Report,' Swallow's First and Second Annual Report, Geol. Survey Missouri, 1855, 

 pt. 2, p. 185. 



2 Report Geol. Survey Illinois, 1866, vol. ii. p. 274. 



