128 EXPLORING EXPEDITION FEOM SANTA Fft 



I have not seen very satisfactorily the hinge of this shell ; but, as near as can be 

 determined from impressions left in the matrix, it appears to present the characters of 

 the genus Crassntella. It is chiefly remarkable for thickness of the valves in proportion 

 to the size of the shell. 



Local/ft/ and position. Pope's Well ; top of Middle Cretaceous of New Mexican 

 section. 



Genus CYPRIMERIA, Conrad. 



CYPRIMERIA? CRASSA, Meek. 



I'late I, figs. 8 a, I, c, tl. 



-+ 



Shell lenticular, rather thick, moderately convex; beaks distinctly compressed, and 

 projecting very slightly beyond the regular curve of the cardinal margin; anterior mus- 

 cular impression narrow-subovate and acute above ; posterior broader, and rhombic- 

 subquadrate ; pallial line distinct, with a very faint sinuosity, or mere truncation, 

 immediately under the posterior muscular impression; surface merely marked by con 

 centric strise. 



Height, 1.93 inches; length, or antero-posterior diameter, 2 inches. 



I am not altogether sure that this species will be found to agree exact/// in its 

 generic characters with Mr. Conrad's genus Cyprimeria, as its hinge-teeth do not seem 

 to agree in some slight details with that of the type of that genus. Indeed, on first 

 preparing a description of it for this report, I had proposed a provisional subgeneric 

 name for it; but, on revising the MS., and comparing the figure, I find it resembles 

 Cyprimeria at least so nearly that I have concluded to refer it to that genus. This has, 

 however, been done partly because I am unwilling to propose a new name without 

 having the type-specimen at hand for further study, it being in New York, and the cir- 

 cumstances being such that I have to revise the MS. in great haste.* 



The hinge of this shell may be described as follows: hinge-plate broad and 

 flat; anterior teeth compressed, the two in the right valve close together, and re- 

 ceiving that of the left between them, ranging very obliquely forward and downward; 

 posterior tooth of righfr valve thicker, ranging obliquely backward and downward, 

 grooved along. the middle, and fitting between the posterior teeth of the left valve. 



Locality and position. Pope's Well; top of the Middle Division of the New Mexican 

 Cretaceous section. 



Genus CARDIUM, Linn. 



CARDIUM BELLULUM, Mock. 



Plate II, figs. C a, 1>. 



Shell small, thin, ovate, a little oblique, gibbous, the most convex part of the 

 valves being somewhat above the middle; beaks elevated, rather slender, incurved, 

 slightly oblique, and located a little in advance of the middle; hinge very short, anterior 

 and antero-basal margins forming together a semi-oval or nearly semicircular curve ; pos-- 

 tero-basal border prominent, and somewhat narrowly rounded; anal margin obliquely 

 truncated above, so as to form with the slope in front of the beaks an angle of nearly 



* Since writing the above, I have again examined the type-species, and find that it agrees so nearly with Ci/i>riin<-i-i.i 

 that, so far as they show, there would seem to bo no satisfactory reason for separating it. 



