CHONETES OF THE CORNIFEROUS LIMESTONE. lai 



Dorsal valve unknown. 



Surface marked by regular subequal rounded or subangular striae, which 

 are often irregularly bifurcated towards the margin or increased by 

 intercalations, and sometimes are nearly simple throughout their 

 length below the umbo, those of the cardinal extremities being very 

 irregular or nearly obsolete. Hinge-line marked on each side of the 

 centre by four or five strong tubular spines which are directed obliquely 

 outwards. 



The sinus in the ventral valve is not uniform, and though evidently a 

 normal character where it occurs, it cannot be relied upon for characte- 

 rising the species. 



Thig species resembles the C. hemispherica; but the form of all the specimens 

 is nearly semicircular, the cardinal extremities nearly "flat, and it is never so gib- 

 bous on the.umbo, while the striae are finer and the cardinal spines more oblique. 



In the surface markings, this species is more nearly like C. coronata, but its 

 form in the specimens known is quite distinctive. 



Geological fonnation and locality. In the Corniferous limestone, near Williams- 

 ville ; Clarence-hollow ; and Stafford, New- York ; and in the same limestone at 

 the Falls of the Ohio. 



Chonetes lineata. 



PLATE XX. 



Strophomena lineata : Vanuxeh, Geol. Report of the 3d District New-Tork, p. 139. f. 6. ( The figure 



6 is placed by mistake at the side of a section of Ichthyodorulite, f. 7.) 

 Chonetes glabra .- Hall ia Tenth Report on the State Cabinet, p. 117. 1857. 

 Compare Strophomena crebrUtriata, Conead, Jour. Acad. Nat. Sciences, Philadelphia, Vol. viii, pa. 254, 



pi. 14, f. 3. 

 Also Chonetet tcitula, Tenth Report on the State Cabinet, p. 147. 

 Also Strophomena lineata, Cohbad, Annn 1 Report, 1839, p. 64. 



Shell subhemispheric, semioval in outline, with the cardinal line 

 equalling or greater than the greatest width of the shell below. 



Ventral valve very convex, often ventricose, a little flattened in the 

 middle, regularly curving to the front and lower lateral margins, more 

 abruptly depressed at the sides, with the cardinal angles somewhat 

 flattened and often a little deflected to the ventral side. 



[ PAI..«0NT0L00y IV.] 16 



