I'.il) CH3TON-RAD8IA. 



Carpenter's opinion of the small importance of the character upon 

 which this Lrroiip is founded, is fully supported by the material 

 studied by myself. lie writes as follows: "The bi- or tri-slitting 

 of the lamina 1 appears to me a character of very secondary impor- 

 tance, as Ix-iiiLf merely numerical, not structural, and as being very 

 variable even in the same specimen. In one specimen of Dr. Gray's 

 type which I received from Mr. Cuming, only one r<i/r> /mil fm> >///.< 



-h >/'/<; most of the other valves had one only ; sometimes a 

 second slit was seen on one side. For such a specimen it would have 

 been as useless to establish a genus as for C//. i'!i-i/n/ntu., or for C. 



a 1 1 in which Dr. Gray found the same abnormality (vide P. Z. 

 S. 1847, p. 127). Another specimen of C. burnt^ii had the valves 

 either withone slit or with two slits on each side, or with one on one 

 side and two or three on the other. Under these circumstances I 

 cannot regard the number of slits as a generic character." 

 Compare alse the notes under C. 



Key to species of Ji<n1*i'i. 



<i. Surface smooth, goodwill. 



tin. Surface sculptured with riblets. 



b. Ribs strong and coarse ; color black-olive, uniform, 



aulcatus. 



/>!>. Riblets fine; color variegated. 



c. Ribets of central areas nearly obsolete ; of lateral areas 



irninose, Imrin-xii. 



cc. Riblets of central areas fine, distinct ; shell olive mottled 



with dark, . 



C. BAI:NI>H ( iray. PL 29, figs. 10,^1, 12. 



Shell oval, J/y,,v.<x/f/, scarcely carinated. Black-brown, yellowish 

 toward the ridge where each valve generally has a dark triangular 

 spot, ami having a butt-white longitudinal stripe on each side; 



Lfirdle L'lven. 



areas raised, sculptured "/'//< nlnmt (5 in-i-i/utti,-, >n,, 

 ///o//x nulinfinfi ///>.>-. Ccnfriif OfOtU .<>-ii/j,fii,-><l ////// 

 longitudinal /-/'////Vx, .v//AoA.vo///r fmnn-il tli> i1nr*nl /vWy, and some- 

 what latticed by growth-lines. Knd valves having radiating 

 nodulous ribs; mnfm <n tli< j,,,.^, ,',,,, r<ilr, very ,,<r f In- front in<r,-(/i/i. 

 Interior whitish ; sinus finely and rather unevenly toothed. 

 rioi \al\c haviiiLr l."i-li;, central valves 2, (occasionally 1 on 



