258 THE VOYAGE OF H.M.S. CHALLENGER. 
column 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 ease, 
and its horizon really Cretaceous, this species is of interest as beimg 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 by 
Meneghini and others. Among these is the Apiocrinus 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. 1 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. Ido not see how it can possibly be 
placed in the same genus as Conocrinus thorenti or Rhizocrinus rawsom 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 species, 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 Pourtalés 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 difference, 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 
different. That of Belemnocrinus is pentagonal, consisting of short joimts with crenu- 
lated faces; 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 Palsozoie 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 florifer, seems to have borne successive 
1 Atti della Soc. Tosc. di Sci. Nat., vol. ii. p. 53. 2 Paleontologie, Bd. i. p. 392. 
8 Revision of the genus Belemnocrinus, and description of two new Species, Amer. Journ. Sci. and Arts, 1877, 
vol, exiii, p. 255. 
