258 THE VOYAGE OF H.M.S. CHALLENGER. 



columa surmounted by the basal plates." His figure shows five of these uppermost stem- 

 joints, which are all low and discoidal ; and it consequently appears to me that the fossil 

 should be referred to Rhizocrinus rather than to Bourgueticrinus. If this be the case, 

 and its horizon really Cretaceous, this species is of interest as being the only known 

 instance of a Cretaceous Rhizocrinus. 



On the other hand, Bourgueticrinus although abundant in Cretaceous deposits, is not 

 certainly known to occur in any Tertiary formation. Some of the types described under 

 this generic name from the Italian Tertiaries have been referred to Conocrinus b)^ 

 Meneghini and others. Among these is the Aioiocrinus cornutus of Schafhautl, which 

 was doubtfully referred to Bourgueticrinus by Meneghini;^ though Zittel,^ while describ- 

 ing its calyx as "niedrig schiisselformig," spoke of it as Conocrinus cornutus. I have 

 been enabled by the kindness of Prof Zittel to examine the calyx of this species for 

 myself ; and I was interested in finding its shape to be very like that of a singular bowl- 

 shaped calyx from the London Clay which is preserved in the Natural History Museum. 

 This has relatively large radials and low basals. I do not see how it can possibly be 

 placed in the same genus as Conocrinus thorenti or Rhizocrinus rawsoni with their 

 elongated calyces mainly formed by the long basals ; and I think that it will be necessary 

 to establish a new genus for the reception of these two sjjecies, to which others will 

 probably be added when the calyces are found corresponding to some of the other Tertiary 

 stem-joints that are now referred to Bourgueticrinus in default of further evidence, e.g., 

 Bourgueticrinus didymus, Schaur. 



Rhizocrinus was supposed by Pourtales to have a considerable resemblance to the 

 genus Belemnocrinus from the Burlington limestone of Iowa and Illinois. Wachsmuth 

 and Springer ' have spoken of this resemblance as being very close and interesting, and 

 stated that " the most important diff'erence, and indeed the only essential distinction 

 between these genera in their external structure, is found in the solid proboscis and 

 covered dome of Belemnocrinus." It appears to me, however, that the American 

 authors lay too much stress on the fact that the calyx is formed in both genera of five 

 long and narrow basals, and that they have overlooked other and more important 

 structural characters. In the first place the stems of the two types are totally 

 difl^erent. That of Belemnocrinus is pentagonal, consisting of short joints with crenu- 

 lated feces ; while the stem-joints of Rhizocrinus are elongated and more or less dice- 

 box shaped, with the well known, enlarged and elliptical ends. Stem-joints articulated 

 like those of Rhizocrinus do indeed occur in the Palaeozoic Platycrinus, and under these 

 circumstances we may fairly expect that any genetic relationship between Belemnocrinus 

 and Rhizocrinus would have manifested itself in this character. But the stem of 

 Belemnocrinus, at any rate of Belemnocrinus jlorifer, seems to have borne successive 



' Atti della Soc. Tosc. di Sci. Nat., vol. ii. p. 53. ^ PalKoiitologie, Bd. i. p. 392. 



' Revision of the genus Belemnocrinus, and description of two new Species, Anier. Journ. Sci. and Arts, 1877, 

 vol. cxiii. p. 255. 



