OF CONCHOLOGY. 



13 



present species they are minute, acuminate and point forwards. 

 The truncation of the cardinal margin of our shell is also a 

 marked difference ; Avhile the surface markings of the two species 

 are entirely unlike. 



CARDINIA. 

 ? C. PONDEROSA, Gabb. — PI. 6, fig. 11, 11a. 



Shell large, elongate, sub-oval, very thick ; beaks a little 

 more than a fourth of the length from the anterior end, very 

 small, placed close together ; ends broadly and nearly equally 

 rounded, anterior a little the narrowest, cardinal margin slight- 

 ly arched ; base very broadly convex, nearly straight ; imme- 

 diately under the beaks the outline is very slightly emarginate ; 

 lunule none ; ligament moderate in size, narrow, not prominent. 

 Surface marked by rough, irregular lines of growth closely 

 placed. Internal margin entire ; pallial line strongly marked ; 

 muscular scars shallow. 



Length, 3-7 in. ; width, 2-25 in. ; diameter of both valves, 

 1-6 in. ; thickness of shell in the middle of the valve, '28 in. 



Found by Dr. A. Blatchley at New Pass, near Austin ; Trias. 

 I have seen several impressions in the slates of Star Canon, 

 which I believe to belong to the present species, but all are 

 more or less distorted and flattened, and in none are there any 

 portions of the shell preserved. 



The specimen from which the above description is taken is 

 in a remarkably good state of preservation, the valves are in 

 contact, and, although slightly broken, show the entire outline 

 and all of the other specific characters perfectly. By careful 

 manipulation I succeeded in not only separating the valves, but 

 in detaching most of the shell from the interior mould, although 

 the entire shell substance is extremely friable, being replaced 

 by crystals of dolomite. I was not, however, fortunate enough 

 to see all of the hinge, a portion of it crumbling away. So far 

 as could be ascertained, it possesses more the appearance of 

 Cardinia than any other described genus, and I have therefore 

 so referred the species, despite the very thick shell structure. 

 A marked peculiarity of the crystallization is that the crystals 

 are deposited in two distinct layers, a well-defined plane of 

 separation running parallel with, and about mid-way between 

 the outer and inner surfaces, throughout almost the entire shell. 



POSIDONOMYA, Brown. 

 P. Blatchleyi, Gabb.— pi. 6, fig. 12. 



Shell large, flattened, obliquely sub-circular ; beaks small. 



