118 PALEONTOLOGY OF NEW- YORK. 



CHONETES OF THE UPPER HELDERBERG AND HAMILTON GROUPS. 



Clumctes lieinisplierica. 



PLATE XX. Fio. 6. 



Ckonelti kemitpheriea : Hail, Tenth Report on State Cabinet, p. 116. 1867. 

 Compare Strophomena gibbota, Cosead 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. 

 Vbntkal valve very ventricose or subhemisjjheric, 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 strias, 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 papilla 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. 



