• 



the Morphology of the Blastoidca. 241 



identical, basals, radials, and orals entering into its composi- 

 tion in varying proportions. But while the ventral surface or 

 "summit" of Codaster is marked by eight groups of hydro- 

 spire-slits, with from five to twelve slits in each group, that of 

 Stephanocrinus is absolutely free from any thing of the kind. 

 In Orophocrinus and in Phcenoschisma the hydrospire-slits 

 are more or less visible externally, as they are in Codaster. 



In Pentremites, Pentremitidea, Troostocrinus, Granatocrinus } 

 Schizoblastus, and other genera they may be exposed by re- 

 moving the lancet plates from the ambulacra. But in Stephano- 

 crinus, as perhaps also in I V icoelocr i 'nus , even tiiis extreme 

 measure fails to reveal their presence, and their nature must 

 remain uncertain until specimens are found in a sufficiently 

 good state of preservation for sections to be made of them. 

 S. pulchellus was first described as a Cadaster bv Miller and 

 Dyer; and Hall transferred it to Stephanocrinus with a ?. 

 But his statements respecting the identity of the two genera 

 are utterly incomprehensible to us. Neither his description of 

 Stephanocrinus nor that of Miller and Dyer contains any 

 mention of the hydrospiral apparatus which has been described 

 in Codaster by M'Coy, Romer, Rofe, Shumard, Lyon, and 

 also by Prof. Hall himself! 



The same remarks apply to the Codaster pentalohus of Hail* 

 from the Niagara group of Waldron, Indiana. It appears to 

 us to be the upper portion of the calyx of a Pentremitidea, 

 broken across at the basiradial suture. The Codaster grati- 

 osus of Miller f is also a very doubtful representative of the 

 genus. The only known specimen is an exceedingly perfect 

 cast from the Keokuk group (Carboniferous) of Missouri. It 

 is said to have no orals ; but there are " ten marginal supports 

 of the interambulacral areas, one being placed upon each side 

 of the ambulacral spaces." What thesi may be we will not 

 venture to say ; but we are surprised to find no mention of 

 any casts of the hydrospires, and are therefore sceptical about 

 the CWaster-nature of the specimen. 



The following are the known species of Stephanocrinus : 



Stephanocrinus angulatus, Conrad. Niagara group 



(Upper Silurian), New York. 

 S. gemmiformiS) Hall. Ditto. 

 Codaster pulchellus, Miller & Dyer. Niagara group, 



Indiana. 

 Stephanocrinus osgoodensis, Miller. Ditto. 



t 



Indiana Report, pp. 280, 281, pi. xv. fig. 16. 



Journ. Cincinn. Soc. Nat. Hist. vol. ii. Jan. 1380, pi. 



xv. %. 5. 



Ann. & Mag. N. Hist. Ser. 5. Vol. xi. 17 



