!»• PALEONTOLOGY OF NEW- YORK. 



cystites (and Heterocystites, which is possibly a crinoiJ ). In the present 

 volume are added Lepadocrinus, Spharocystites, and Anomalocystites. 



Mr. Billings, of the Canada Geological Survey, has described in his 

 Report, now in press, Glyptocystites, Pleurocystites and Malocystites, from 

 the Lower Silurian rocks. 



The following notice of the principal genera of Cystidians at present 

 known, with some of their leading characteristics, may not be uninteresting 

 in this place. 



Hemicosmites ( Von Buch, 1840). Body composed of four series or ranges of plates : 



basal plates four, two narrow pentagonal and two broad hexagonal ; second 



series, six plates ; third series, nine plates ; fourth, or supraovarian sei'ies, 



eight plates. Ovarian pyramid five-valved : mouth central. Arms noae. 



This genus is interesting from its relations with Caryocrinus ; and forms, with that genus, 



% well-marked passage from the Crinoidese to the Cystideae. 



H. pyriformis, H.? ohlorigiis and HA squamosvt are Lower Silurian species. 



CARyocYSTiTEs ( Vou Bucli ). Body spheroidal or irregular, composed of five ranges 

 of plates; the base having four, of which two are large and two small. 



This genus is by some palaeontologists included under Echinospfuerites, and differs mainly 

 in the less number and definite order of arrangement of the plates. 



C. davisi, C. granatum, C. litchi, C.l mmiitus, C. pyriformis, are Lower Silurian species. 



EcHiKosPH^RiTEs ( Walilenbcrg, 1821 ) ; Sphjeronites ( Hisinger, 1837 ). Body 

 spherical, composed of a great number of plates, which are irregularly dis- 

 posed : basal plates six. Oral and anal orifice at the summit. Ovarian orifice 

 on the postero-lateral portion of the upper hemisphere of the body, in a line 

 with the mouth. Arms none. Surface of plates striated with ridges radiating 

 from the centres of the plates. 

 E. arachnoides. E. atirantium, E. ballicus, E. pomum, EJ punctalus, E. tesseltalus : 

 these are all Lower Silurian species, with the exception of E. tessellatus of Phillips. One 

 or more species of this genus have been found abundantly in Canada. The specimens from 

 Escanaba river, described by the writer, belong probably to this gcnu.«. 



Cbyptocri KITES (Von Buch ). Body rotund, subhemispherical, composed of three 

 ranges of plates : basal plates three; second series five; third series (according 

 to Von Buch) five. 

 C. IcBvit : a Lower Silurian species. 



