FREE INSTITUTE OF SCIENCE 



TERTIARY FAUNA OF FLORIDA 



I 139 



Family LEPTONID^. 

 Genus LEPTON Turton. 

 Lcpton Turton, Dithyra Brit., p. 61, 1822. Type L, squamosum Montagu. 

 Eupolcme Leach, Moll. Gt. Brit., p. 279, 1852. Same type. 



Neolepton Monterosato, Nuova Revista, 1875, p. 12, nota; Nom. Conch. Medit., p. 15, 

 1884. Type Lepton siilcatulum Jeffreys. 



In this genus we have the hinge composed in the left valve of an anterior 

 lamella at the umbonal end of which is a nascent cardinal or " hook" which 

 may or may not be completely detached from the lamella ; behind this is a stout 

 internal resilium, behind which is a posterior lamella which rarely becomes 

 obsolete. In the right valve a pair of lamellae on each side of the resilium is 

 disposed in such a manner as to form a socket for the lamella of the opposite 

 valve. The hinge is concentrated in comparison with that of most of the 

 Leptonacca, the lamellje are short, the resilium is short, stout, and nearly 

 central. In the typical species there is only one cardinal " hook," and that is 

 in the left valve. The shells are usually somewhat compressed, subquadrate, 

 and polished, with a minute surface-sculpture, punctate or sagrinate ; the beaks 

 are nearly central and erect. The anatomical characters are remarkable, but 

 it is only necessary to state here that the mantle is reflected over the valves 

 which it normally covers to a greater or less extent. 



The hinge of all the Lcptonacea is fundamentally based on the same plan, 

 the different genera merely exhibit modifications of detail. The notion that 

 any relation to Mactra, Cyrena, and other alien genera is shown by these modi- 

 fications is unwarranted and superficial. The apparent resemblances are not 

 genetic, but due to convergence, except in so far as they exhibit features com- 

 mon to the nepionic stages of Teleodesmacea in general. The careful student 

 will see in the hinge of Lepton relations to Scintilla, Myllita, Bornia, etc., but 

 it is impossible to say which, if any, of these predominates. Hardly any three 

 of the species have a precisely similar dentition, and the sections hereinafter 

 enumerated must therefore be considered as merging peripherally into each 

 other. 



.Section Lepton s. s. Type L. squamosum Mtg. 

 Characters mainly as given in the generic diagnosis, an anterior cardinal 

 hook in the left valve, none in the right valve. 



Section Neolepton Monterosato. Type L. snlcatnluin Jeffreys. 

 Shell inflated, concentrically striate, more or less inequilateral, impunctate ; 

 hinge essentially the same as in Lepton proper. 



