FOSSILS OF THE KKOKI'K (IlIOl'P. 521 



the angles distinct : aperture subquadrangular, or subrhoui- 

 bie and contracted ; lip very profoundly notched or divided 

 at each corner, so as to form four triangular flaps or ap- 

 pendages, with inflected lateral margins. Surface orna- 

 mented with numerous tine, crowded, transverse cost*, 

 or stria\ which arch slightly towards the aperture in 

 crossing each side, without any interruption or backward 

 curve at the obscure mesial sulcus ; cost* regularly cre- 

 uate, and separated by slightly wider depressions near the 

 middle of the shell, but much more crowded towards the 

 aperture ; depressions between the cost*, with very ob- 

 scure, minute transverse furrows, coincident with the cren- 

 ulations of the cost*. 



Length about 4.25 inches; greatest breadth, measuring 

 diagonally across between opposite angles of an obliquely 

 compressed specimen, 1.63 inches; greatest breadth of one 

 side, 1.23 inches. Xuinber of costa? in the space of 0.20 

 inch, near the middle of the shejl, 10 ; do., near the aper- 

 ture, 20 inch. Xuinber of crenulatioiis in the same space 

 on each of the cost*, 20. 



In general appearance the species of this genus often present com- 

 paratively little difference, and not imfrequently they so closely resem- 

 ble each other in their ornamentation as to require a careful comparison 

 to distinguish them. Probably the most marked peculiarity of this 

 species is the presence of a deep, sharply defined notch at each corner 

 of the aperture in the lip, extending down nearly an inch from the mar- 

 gins of the aperture, and widening upwards, so as to divide the lip into 

 four subtriangular flaps, which bend a little inwards, so as to contract 

 the aperture and cause the widest part of the shell to be an inch or 

 more below its upper extremity. Our specimen is not in a condition to 

 show whether these flaps are pointed or truncated at the extremity. 



This species will be readily distinguished from our C. multicostata, by 

 its coarser and more widely separated, as well as more coarsely creuate 

 stri;e, even where the deep notches of its lip cannot be seen. 



It is possible this may be the form figured by Dr. Emnions in his 



Manual of Geology, under the name C. Verneuilii ; but as he gave no 



ription, and but a rough wood-cut of the species so named by him, 



we have no means of knowing its characters. His figures, however. 



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