GENUS APIOCYSTITES. 315 



The ovarian aperture is situated over the right superior angle of the hexa- 

 gonal basal plate, and the space is excavated from the upper margin of 

 the plates of the third range and the lower margin of one of the fourth 

 range. 



The pectinated rhombs upon the right side of the ovarian aperture occupy 

 the adjacent margins of two plates, and are on the same parallel with 

 the aperture. The other pectinated rhombs are not preserved in the 

 specimen. 



The plates of the four lower ranges are longitudinally ridged in the 

 middle, and in their perfect condition have probably had a central node. 

 The circa-ovarian plates, and those of the centre of the summit or apex 

 have not been determined. 

 The specimen described is a cast, but so well preserved as to indicate 



very satisfactorily its most important characters. It is a more elongate 



form than any cystidean of this group {Pseudocrinites, Apiocystites, etc.) 



that I have seen from American rocks. 



Formation and locality. In the Racine limestone ( Niagara group) at 



Kacine, Wisconsin. 



GENUS HEMICOSMITES (Von Buck). 



This genus was established by Yon Buch for a fossil figured by Pander 

 under the name of Echinosphcerites malum. 



The body consists of four series of plates ; the basal series containing 

 four plates, of which two are hexagonal and broad, and two narrower and 

 pentagonal, similar to those of Caryocrinus. The second or subradial 

 series consists of six plates, which are likewise very similar to those of 

 Caryocrinus, except that three instead of two are truncated at their upper 

 margins ; and two of them are excavated on their upper adjacent lateral 

 angles for the ovarian aperture which lies between these and the base of 

 one of the plates of the succeeding range. 



In the third range of plates this genus differs from Caryocrinus in having 

 nine instead of eight plates : the ninth comes in by a truncation of a plate 

 of the second range, which corresponds to the plate directly opposite the 

 ovarian aperture of the other genus. 



The mouth is represented by VoN Buch as central. It is not known 

 to possess arms or tentacula. 



Among the fossils of the Niagara group in New- York, are some separated 

 plates which I have supposed may belong to this genus ; but their relations 

 ha^-e not been fully established ; though I have little doubt that farther 

 examinations in some of the more prolific localities will show the occur- 

 rence of this genus. 



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