144 STUDIES IN GEOLOGY, No. 3 



of concentric growth-lines, which are of irregularly spaced 

 folds simulating concentric ribs. Lunule ovate, denned by 

 a slightly impressed line; there is no escutcheon. Hinge 

 normal, the cardinals well developed and distinct in the 

 right valve; in the left valve the anterior lateral tooth is 

 highly developed, taking the shape of a flattened dowel-pin, 

 the flat sides horizontal, the posterior edge straight, and 

 the anterior edge curved, the tooth thus having the shape of 

 a half-D, viewed dorsally. This tooth is received into the 

 usual socket in the right valve. Inner shell unknown. 

 Length (estimated) 25-27; height, 20.5; (semi) diameter 

 8 mm. 



This species is much larger than any of the fossils of 

 the genus listed from the Americas. It has an interesting 

 development of the strong anterior lateral tooth character- 

 istic of the genus, and may be recognized very readily by 

 that feature as well as by its size. The hinge of the right 

 valve is that characteristic of the common Transennellas, 

 excepting possibly the strong development of the socket 

 which receives the peculiar anterior lateral tooth of the 

 opposite valve. None of the members of the genus from 

 the Floridian, Antillean, or Atlantic Miocene are closely 

 similar. It is unfortunate that both of the two specimens 

 in the Hopkins collection lack the anterior and posterior 

 extremities, and a comparison of the outline is thus subject 

 to revision; however, the visible portions indicate that it is 

 probably less triangular than the known fossil species. It is 

 considerably more inflated and larger than any Miocene 

 species thus far described. 



The most closely similar species is T. joaquinensis Ander- 

 son and Martin, 160 from the lower Miocene of Kern River, 

 California, which differs in being smaller and more delicate, 

 with the left anterior lateral tooth elongated diagonally 



lfl Proc. Cal. Acad. Sci., 4th sen, vol. 4, p. 60, pi. 3, figs. 6a, b, 

 c, 1914. 



