280 PROCEEDINGS OF THE ACADEMY OP [1879. 



11 RHOPALOCRINUS nov. gen. 

 (poVaXov, a club, xpivov, a lily.) 



Schultze, in his Monogr. d. Echinod. d. Eifl. Kalkes, p. ^9, de- 

 scribes a form under the name of Taxocrinits gracilis, which is 

 very interesting, inasmuch as it combines, to some extent, the 

 characters of several families. There are only five arms, which 

 remain simple throughout their entire length, forming a straight 

 line with the radials a peculiarity found in no other genus of the 

 Ich.thyo'cri^idx. This attracted the attention of Schultze, who 

 suggested either a modification of the genus Taxocrinits, so as to 

 admit this species, or the recognition of a new genus. In the 

 former proposition we cannot concur, as it seems to us we must 

 admit such peculiarities as exist in this species to be generic dis- 

 tinctions, or throw all forms of the Ichthyocrinidse into a single 

 genus. As to this genus, we even entertain some doubts whether 

 it belongs to the same family. 



Our genus Rhopalocrinus, with R. ( Taxocr.) gracilis Schultze, 

 as type, agrees in general form rather with Cupressocrinus, Sym- 

 bathocrinus and Graphiocrinus representing as many distinct 

 families than with Taxocrinits; but it differs from all of them in 

 having a series of small plates inclosed between the rays. These 

 plates, whjch Schultze calls " interbrachials," fill up, according to 

 his description, "the intermediate spaces to the top of the second 

 radials," being thus included within the body. If we were sure 

 that this was the case, we should, notwithstanding the simple 

 arm structure, place Rhopalocrinus, without hesitation, under the 

 Ichthyocrinidse; but, as it is, the preservation of these parts is 

 not so satisfactory as to exclude another interpretation. The so- 

 called interbrachial plates are seen only in one interradial space, 

 and, as all successive plates from the radials to the tips of the arms 

 have the same form (with the exception of the first one, which is 

 three to four times shorter, but otherwise similar), and an almost 

 circular articulating surface, which has never been observed in 

 plates forming part of the body, it seems quite possible that all 

 branches were free, and that the small plates were deposited 

 accidentally, being either plates of the vault, or perhaps remains 

 of tiie pieces which once oovered the arm furrows. 1 This of 



1 The type specimen with Dr. L. Schultze's entire collection is now in 

 the Museum of Compar. Zoology at Cambridge. 



