18*79.] NATURAL SCIENCES OF PHILADELPHIA. 365 



It is succeeded by two rows of regular interlocking plates. The 

 arms are very heavy, rounded on the outside, continuing of the 

 same size to near the top, where they taper to a sharp point. The 

 articulation between the radial and brachial plates is on the same 

 principle as in Eupachycrinus. There is a narrow single line 

 across the entire width of the plate, and the outer edges of both 

 plates adjoining it are so strongly bevelled in the typical species, 

 that if the arms were open, nearly one-half of the brachials would 

 rest upon, and be supported by the sloping face of the radials. 

 Column round. 



The total absence of anal plates in this and the preceding sec- 

 tion of the genus, distinguishes it readily from any other of this 

 family, but at the same time raises a reasonable doubt whether 

 Erisocrinus and Stemmatocrinus possessed a solid ventral append- 

 age, and, therefore, whether they belong to the Cyathocrinidse, or 

 even to the Palasocrinoidea. We have, so far, no knowledge what- 

 ever of the construction of the actinal or oral side of the body; 

 whether it had an open mouth or was firmly closed by plates or 

 scaly integument; and if it had not been for their marked resem- 

 blance to Eupachycrinus in which a ventral' tube has been ob- 

 served, and that both were representatives of the same geological 

 age, living under the very same conditions, we should have felt 

 strongly disposed to place the whole genus with Encrinus, with 

 which it has, indeed, both in body and arms, the closest affinities. 

 That Erisocrinus and Stemmatocrinus have only one brachial, 

 and Encrinus two, is not material, and is, at the most, only of 

 generic importance; but in Encrinus the aboral side of the body, 

 or the plates which in all Cyathocrinidae constitute the calyx, form 

 almost a flat disc at least do not extend beyond the basal plane 

 and this is the only important distinction which can be dis- 

 covered between the two forms in the fossil state. This, how- 

 ever, may involve important structural modification in the internal 

 anatomy of the animal, and probably shut out Encrinus entirely 

 from the Palaeocrinoidea. 



Geological Position, etc. Stemmatocrinus is onty known from 

 the limestone beds of Mjatschkowa, where Prof. Trautschold dis- 

 covered the only species. 



1867. Stemmatocrinus cernuus Tniut.=ch. Bulletin d. I. Soc. d. Nat. de Moscou, 

 1867; also Monogr. d. Kalkbr. v. Mjatschkowa, 1879, p. 125, pi. 14, fig. 12. 

 Upper part of Subcarbon., near Moscow, Russia. 



