TRANSACTIONS OF WAGNER 

 I 156 



TERTIARY FAUNA OF FLORIDA 



tained in a varietal sense. The Californian specimens are more like those from 

 Britain, though often difficult to discriminate from the young of K. Laperousii. 



Genus THECODONTA A. Adams. 



Thecodonta A. Adams, Ann. Mag. Nat. Hist., xiii., p. 308, 1864. Type T. Sieboldii A. 

 Adams, op. cit., Japan. 



Shell oval, very inequilateral, the beak nearly terminal in front, hinge with 

 an arcuate short left anterior lamella, behind which is a triangular shelf for the 

 resilium, the posterior lamella long, narrow, separated from the dorsal margin 

 by a narrow groove, the distal portion slightly elevated, then depressed, and 

 rising beyond the depression in a second elevation corresponding to a posterior 

 lateral ; pallial area faintly radiated, basal margin entire ; right valve un- 

 known. 



The long side in this group is posterior, while in Rochefortia it is anterior 

 and in this group the posterior and anterior teeth are very unequal in length. 

 I am indebted to Mr. Edgar A. Smith of the British Museum for a careful 

 drawing of the hinge of the type specimen. 



PSubgenus Serridens Ball. (Pristiphora Cpr., 1866; not Blanchard, 1835.) 



Shell like Thecodonta, but the resilium planted on the inner surface of the 

 valve, not on a shelf, the posterior lamella simple and the teeth proximally 

 finely cross-striated. Type Pristiphora oblonga Cpr., Proc. Cal. Acad. Sci., 

 iii., p. 210, 1866. San Pedro, California. 



In 1864 (Suppl. Rep. Br. Assoc. for 1863, pp. 611, 643) Carpenter used the 

 name Pristes for an undescribed species of shell allied to Rochefortia, but when 

 he came to describe it, regarding Pristes as preoccupied (Latham, 1794), he 

 proposed the name Pristiphora (Proc. Cal. Acad. Sci., iii., p. 210, 1866, sole 

 example P. oblonga Cpr., loc. cit.; not Pristiphora Blanchard, Hymenoptera, 

 1835), which was also unavailable. 



PSubgenus Dicranodesma Ball. 



Shell rounded-trigonal, in general like Serridens, but with the anterior 

 tooth elevated and conical, the hinge-plate excavated, the posterior lamella 

 smooth, stout, and elevated in the left ; thin, high, and marginal below a wide 

 groove in the right valve ; muscular impressions rounded, small, dorsally 

 situated; pallial area smooth, basal margins entire. Type D. calvertensis 

 Glenn. Miocene of Maryland. 



I am in some doubt as to whether this form and Serridens are to be re- 

 ferred to Thecodonta as subgenera, or should form a group apart. The chief 



