THYSANOCRINID^. 191 



biserial ; pinnules long. The first interbrachial large, resting upon the 

 sloping upper corners of two radials and against the costals. There are two 

 plates in the second range, and often smaller ones above, which connect with 

 the plates of the disk. The anal side considerably wider ; the first plate 

 large, hexagonal, resting upon the posterior basal ; the second range contain- 

 ing three plates. Some species have an uninterrupted row of anal plates all 

 the way to the anal opening. Interdistichals generally represented and rather 

 large. Structure of the ventral disk and position of the anus only known 

 in one species. (See Thi/sanocrinus inornatus) column round or obtusely 

 pentangular. 



Disirihdion. — Eestricted to the Niagara group of America, the Wenlock 

 group of England, and its equivalent in Sweden. 



Type of the genus. — Thysanocrinus liliiformis Hall. 



Remarks. — We have reduced Dmierocrimis, Glyptaster, TJiysanocrinus 

 and Eucrinus to one genus, finding it utterly impossible to distinguish them 

 generically. There is some doubt, however, by what name the genus should 

 be known. The name Dimerocrimis was applied by Phillips to two species 

 from Dudley, D. decadactyliis and D. icosidactykis. Both were figured but 

 not described, and the figures were poor and did not reveal the character- 

 istics of the genus. A meagre description was given by Muller, who men- 

 tioned " a pelvis," succeeded by 3 X 5 radials, and two series of arm plates. 

 D'Orbigny described it with three basals, succeeded by three rings of plates. 

 From such vague and incorrect descriptions, Hall could not suspect that 

 a species with ^\q basals and infrabasals would be generically identical with 

 species described as possessing three basals and no infrabasals, and we believe 

 he was justified in proposing for his species a new genus. Pictet and 

 Dujardin and Hupe, who accepted both genera, placed them near together. 

 Zittel, however, even refers them to distinct families. We were the first to 

 point out the generic identity of Tliysanocrinus with the forms which are 

 held to represent Dimerocrimis decadactyliis and D. icosidactyluSy but dis- 

 criminated in favor of the older name Dimerocrinus^ which we nov\r think 

 w^as scarcely fair to Hall. Besides, we accepted Glyptaster and Eucrinus^ 

 though with some hesitation, making the latter a subgenus of the former. 

 The name Glyptaster was proposed for a sohtary specimen, described as 

 G, hrachiatus, in which all the plates of the calyx w^ere obscured by matrix, 

 but showing ten spreading biserial arms without visible pinnules, and it 

 was principally upon the absence of pinnules, it seems, that the genus was 



