71 



which Mr. Billings considered as the enclosing sac, sometimes incrusts the 

 Brachiopoda of the same formation. 



" Mr. Niles referred to the interest these specimens afford to the natur- 

 alist, aud gave a brief review of their scientific history and of the theories 

 of prominent investigators. He then proceeded to show the cystidian affi- 

 nities of the species by considering the complication of structure exhibited 

 in the group as a type in geological history. He showed that all the fea- 

 tures of the genus Cyclocrinites are, at the same time, embryonic and 

 cystidian, and stated that so far as he knew, this is the only genus of the 

 family yet discovered in America, although the family is well represented 

 in the Palaeozoic strata of Euroj)e." 



After seeing the above, I wrote to Prof. A. Agassiz, and he kindly sent 

 me three of the specimens which possess the supposed orifices for exami- 

 nation. With all due deference, I do not feel at all convinced that the 

 organs in question are anything more than accidental arrangements of the 

 plates. In the true Cystideans there is usually a small aperture on the 

 summit with a larger one below. This latter, in many species, is provided 

 with a valvular apparatus of five or six angular plates. There is never 

 more than one of those large lateral openings, (in the true Cystideans) 

 but in one of the specimens from the museum at Cambridge there appear 

 to be four ; in another there are three. None of them have, at least to 

 me, the aspect of the ovarian pyramid, as it is called, of the true Cysti- 

 deans. We have (in the Provincial collection) two specimens of P. Halli, 

 with the summits very well preserved, and they do not show any traces of 

 an apical aperture ; neither do they exhibit any signs of ambulacral grooves 

 or arms. 



Pasceolus Halli is covered with a thin integment, about one-third of a 

 line in thickness, of a translucent horny colour, the surface minutely 

 wrinkled but exhibiting no traces externally of a division into plates. It 

 has not the peculiar crystalline fracture of crinoidal plates. When this 

 integument is removed from the fossil, as it is in the Cambridge specimen, 

 the whole of the surface of the coat of the interior is covered, with small 

 polygonal spaces usually a little convex in the centre. Some individuals 

 are incrusted with what appears to be a species of Stenopora. The 

 Russian specimens are often over-grown in the same way, and Eichwald 

 considers this incrustation to be a part of the integument itself. If 

 he be correct in this view, then the structure of this genus is widely 

 different from that of any known echinoderm. It may be that these 

 bodies are akin to Salter's genus Nididites, supposed to be collections 

 of the eggs of some species of mollusca. In that case the coral-like tubes 

 might have exercised the function of small capsules for holding the eggs. 



Eichwald seems to describe Oyclocrinus as having an aperture in the 

 summit, in which case it must be a distinct genus from Pasceolus. He 

 does not figure any specimen showing the orifice, and it is evident that he 



