15® 
PALAEONTOLOGY OF NEW-YORK. 
cystites (and Heterocystites, which is possibly a crinoid). In the present 
volume are added Lepadocrinus, Splicer o cystites, 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 ( Yon Buck, 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 series, 
eight plates. Ovarian pyramid five-valved : mouth central. Arms none. 
This genus is interesting from its relations with Caryocrinus ; and forms, with that genus, 
a well-marked passage from the Crinoidem to the Cystideae. 
H. pyriformis, H.? oblongus and II .? squamosus are Lower Silurian species. 
Caryocystites ( Yon Buc-h ). 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 Echinosphcerites, and differs mainly 
in the less number and definite order of arrangement? of the plates. 
C. davisi, C. granatum, C. lilchi, C.? munitus, C. pyriformis, are Lower Silurian species. 
EciiiNosPHiERiTEs (Wahlenberg, 1821); Sphasronites ( 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. aurantium, E. ballicus, E. pomum, E.? punctatus, E. tessellatus : 
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 genus. 
Cryptocrinites ( Yon Buch ). Body rotund, subhemispherical, composed of three 
ranges of plates : basal plates three; second series five; third series (according 
to Yon Buch) five. 
C. Icevis : a Lower Silurian species. 
