1911.] NATURAL SCIENCES OF PHILADELPHIA. 367 



and crenulate, the crenulations narrow and deep on the posterior 

 margin, triangular in the basal margin, very shallow at the anterior 

 margin. 



Length 29.5, width 24, semidiameter 12 mm.; 30 ribs. 

 31.0, " 25, " 13 " ;29 " 



This species is closely related to the recent West Coast Cardium 

 belcheri Brod., which has ribs of the same peculiar, asymmetrical 

 character. In the Gatun shell there are many more ribs, and the 

 tubercles upon them are shorter and blunt, while in C. belcheri they 

 are more spiniform. 



Cardium lingualeonis Guppy is proportionately narrower and has 

 more ribs, but seems to be rather close to the Gatun species. 



C. stiriatum is, by its complex sculpture, a relatively specialized 

 form ; but it is less advanced than the recent C. belcheri, which is 

 further evolved by the reduction in number of ribs; a large number 

 being primitive in Cardium. C. stiriatum may be an ancestor of the 

 recent species. 



This species was known to Toula by hard internal casts, which alone 

 are found in a layer containing mainly bivalves. The largest of several 

 of these casts before us measures, length 26, alt. 33, diam. 26.5 mm. 



*Cardiuin (Trachycardium) dominicanum Call. 



C. (T.) dominicanum Dall, Trans. Wagner Inst., Ill, p. 1,082. 



Oligocene shale near Gatun. 



Cardium (Trachycardium) dominicense Gabb. 



C. (T.) dominicense Gabb, Geol. Santo Domingo, p. 25; Journ. A. N. S. 



Phila., VIII, p. 344 (Gatun and Costa Rica). 

 Cardium (Trachycardium) gatunense Toula, Jahrb., K. K. Geol. Reichsanst., 



1908, LVIII, p. 720, PI. 27, fig. 4. Not Cardium (Fragum) gatunense 



Dall, 1900. 



Abundant in the Gatun collection we have studied. The specimens 

 agree perfectly with Gabb's type of C. dominicense. 



Cardium (Laevicardium) serratum L. 



Dall, Trans. Wagner Free Inst., Ill, p. 1110. 



The shell seems indistinguishable from those of the Bowden bed 

 and from the recent form. C. apicinum Cpr. from the Pacific is 

 closely related. 



*Cardium (Laevicardium) dalli Toula. 

 Jahrb., p. 722, PI. 27, fig. 6. 



If really distinct from C. serratum, this species will require a new 

 name, dalli being in use for a fine Pliocene species. 



