306 PROCEEDINGS OF THE ACADEMY OP [1885. 



Phylum, ECHINODERMATA. 



Class, PELMATOZOA. 



Subclass, Crinoidea. 



Order, PAL^OCRIXOIDEA. 



Suborder, CAMARATA. 



The Cam ar at a embrace the Platycrinidte, Actinocrinidae and 

 Rhodocrinida?. which in Part II we grouped together under the 

 name Sphaeroidocrinidse, and also the Acrocrinidae and Calypto- 

 crinida?, wliich are here described. 



In a paper on Glyptoerinus and Reteocrinus, Amer. Journ. Sci., 

 vol. xxv, April, 1883, we intimated on p. 267, that we might find 

 it advisable to place Glyptoerinus, Reteocrinus and allied genera 

 in a family by themselves. This had been done by Zittel, and 

 has since been adopted by S. A. Miller, under the name of Glyp- 

 tocrinidflft. Zittel included in this family Glyjdocrinus, Glyptas- 

 ter, Thylacocrinus, Cupulocrinus, Lampterocrinus, Eucrinus and 

 Sagenocrinus, genera all having well developed nnderbasals, with 

 the exception of Glyptoerinus, in which the}- were said to be ru- 

 dimentary. Miller's (jlyptocrinidae contain Archaeoerinus, Cu- 

 pulocrinus, Glyptaster, Lampterocrinus, Reteocrinus and his pro- 

 posed genus Gaurocrinus, all having underbasals, and Glyptoeri- 

 nus, Xenocrinus and his Compsocrinus and Pycnocrinus, which 

 he described as having but one ring of plates below the radials. 



The presence of underbasals has been very generally considered 

 a good family distinction, and it has always been a question of- 

 doubt with us whether we were justified in departing from this 

 rule by placing Glyptoerinus and Xenocrinus, in which under- 

 basals were said to be absent or indistinctly developed, in the 

 same group with Reteocrinus and Archaeoerinus, in which those 

 plates form a more or less important part. The genera which 

 Miller has grouped together, and a few more, asiree remarkably 

 in general aspect, but they differ not only in the matter of under- 

 basals, in the number of basals. but also very materially in the 

 disposition and form of their interradial plates. 



Glyptoerinus was originally described as possessing no under- 

 basals. Hall afterwards discovered minute pieces enclosed by 

 the ring of plates which he had previously designated as basals, 

 and which he now called subradials, taking the small inner pieces 



