NO. 1312. SYNOPSIS OF THE VENERIDJE— BALL. 353 



Genus CALLOCARDIA A. Adams, 1864. 



Type, C. guttata A. Adams. 



Shell ovate, plump, thin, concontrioally striated with more or less 

 involute umbones; pallial sinus nearly obsolete; lunule feebly circum- 

 scribed, not impressed, escutcheon not defined; left anterior lateral 

 received between two obsolete laminae in the opposite valve; three 

 cardinals in each valve not radiating- from a point under the umbo, on 

 the dorsal valve margin; the two anterior left cardinals continuous 

 above and separated from the valve margin b}" a sulcus; the anterior 

 and posterior right cardinals similarly connected, and dorsally sepa- 

 rated by a groove from the margin; the arch of the two left cardinals 

 fits over the middle right cardinal, the arch of the outer right cardinals 

 over that of the two left ones, so that the middle right and the pos- 

 terior left cardinals remain isolated; the dorsal margins beyond the 

 hinge plate, in front in the left and behind in the right, are grooved 

 to receive the beveled edge of the opposite valve. 



In this group the teeth retain in the adult state the conditions which 

 normally obtain in the earlj^ stages of hinge development as shown b}^ 

 Bernard. 



The group is identical with Caryatis (part) Romer, 1862, not of 

 Hiibner, 1816; Yenerlglossa Dall, September, 1S86; and Atopodonta 

 Cossmann, October, 1886. It is distributed in tropical and temperate 

 seas and goes back to the Eocene in time. 



The type was named CaUocardia guttata by A. Adams in 1864. In 

 1888 Mr. Sowerby renamed it Cytherea isocardia on account of the 

 existence of a Oytherea {Oallista) guttata of Romer. The latter, 

 however, was not described until 1866, so that it does not antedate 

 Adams's name. If Romer's form is entitled to specific rank, it will 

 not require a new name, as under the present arrangement it will be 

 referable to the genus Macrocallista^ section ChioneUa. 



Subgenus Agriopoma Dall, 1902. Type, Oytherea texasiana Dall, 

 1892. 



This differs from the typical CaUocardia by its large, heavy, and 

 chalky shells, without the involute umbones or any color pattern, and 

 by the presence of a deep and angular pallial sinus. It is more north- 

 ern in distribution than CaUocardia proper, and more limited in geo- 

 graphical range, though receding to the Eocene in America, The 

 peripheral species indicate a transition in the cardinals of the right 

 valve toward the conditions found in the following group: 



Genus PITARIA Romer (em.), 18S7. 



Type, Venns tumens Gmelin. 



Shell trigonal, plump, concentrically striate or rippled, with an incon- 

 spicuous periostracum and delicate coloration; lunule circumscribed, 



