418 Proceedings of the Boyal Society 
convoluted plate, somewhat in form like the shell of a Scaphander, 
placed vertically in the centre of the cup, in the position occupied 
by the fibrous axis or columella in Pentacrinus and Antedon. Mr 
Billings, the distinguished palaeontologist to the Survey of Canada, 
in a very valuable paper on the structure of the Crinoidea, Cystidea, 
and Blastoidea (Silliman’s Journal, January 1870), advocates the 
view that the plate is connected with the apparatus of respiration, 
and that it is homologous with the pectinated rhombs of Cystideans, 
the tube apparatus of Pentremites, and the sand-canal of Asterids. 
Messrs Meek and Worthen and Dr Lutken, on the other hand, 
regard it as associated in some way with the alimentary canal and 
the function of nutrition. 
The author strongly supported the latter opinion. The perivis- 
ceral membrane in Antedon and Pentacrinus already alluded to, 
which lines the whole calyx, and whose involutions, supporting 
the coils of the alimentary canal, contribute to the formation of 
the central columella, is crowded with miliary grains and small 
plates of carbonate of lime; and a very slight modification would 
convert the whole into a delicate fenestrated calcareous plate. 
Some of the specimens in Mr Wachsmuth’s collection show the 
open reticulated tissue of the central coil continuous over the 
whole of the interior of the calyx, and rising on the walls of the 
vault, thus following almost exactly the course of the perivisceral 
membrane in the recent forms. In all likelihood, therefore, the 
internal calcareous network in the crinoids, whether rising into 
a convoluted plate or lining the cavity of the crinoid head, is 
simply a calcified condition of the perivisceral sac. 
The author was inclined to agree with Mr Bofe and Mr Billings 
in attributing the functions of respiration to the pectinated rhombs 
of the Cystideans and the tube apparatus of the Blastoids. He did 
not see, however, that any equivalent arrangement was either 
necessary or probable in the crinoids with expanded arms, in which 
the provisions for respiration, in the form of tubular tentacles and 
respiratory films and lobes over the whole extent of the arms and 
pinnules, are so elaborate and complete. 
