118 
PALEONTOLOGY OF NEW-YORK. 
CHONETES OF THE UPPER HELDERBERG AND HAMILTON GROUPS. 
Clionetes liemisplierica. 
PLATE XX. Fig. 6. 
Chonetes hemispherica : Hall, Tenth Report on State Cabinet, p. 116. 1857. 
Compare Strophomena gibbosa, Conkad in Annual Geol. Report, 1841, p. 54. 
Shell transverse, semielliptical or somewhat semicircular, the greatest 
width being on the hinge-line, which is often much extended and 
conically auriculate at the extremities. 
Ventral valve very ventricose or subhemispheric, excluding the extre¬ 
mities ; the umbo prominent, rising considerably above the hinge-line, 
with the apex incurved. The hinge-line is marked by three, four or 
more spines on each side of the middle. 
Dorsal valve unknown. 
Surface marked by numerous regular rounded striae, some of which 
bifurcate near their origin and then continue simple throughout their 
length; a few bifurcate on the middle of the shell, and near the margin 
there are sometimes intercalations of other striae. 
The cast of the ventral valve preserves the striae with almost the same 
distinctness as the exterior shell; and the depressions between them 
are marked by distant oblong pores, which indicate papillae of the same 
form on the interior of the shell. 
In a specimen of ordinary size, there are about 50 to 54 rounded 
striae, and 7 to 9 (and rarely 12 or 14 in young specimens) in the 
space of two-tenths of an inch, so few of which bifurcate that the gene¬ 
ral aspect is that of simple striae. 
Some specimens, which appear to be younger individuals, of this 
species, are of moderate convexity, and the striae* are finer and a little 
more angular than in the larger and older specimens. 
The figures 6 a, b, represent the ordinary forms of this species. 
