116 PALEONTOLOGY OF NEW-YOKK. 



154. 17, LEPTjENA ( Species undetermined ) . 



Pl. XXXI. B. Figs. 10 a, b, c. 



Semioval ; greatest width i|, height j\ of an inch ; cardinal line scarcely equalling the 

 greatest width of the shell below ; surface marked by fine radiating striae, which are crossed 

 by fine concentric lines ; striae upon the ventral valve equal and uniform in size ; those on 

 the dorsal valve consisting of larger striae with one or two finer ones between, a single one, 

 larger than tlie others, extending from the beak to the base of the shell ; beak imperforate ; 

 foramen not closed. 



This species presents many characters in common with L. alternata, and is perhaps only 

 the young of that shell. The character of the surface markings is very analogous, differing 

 uo more than might be expected between the young and old individual. The callosity of 

 the ventral valve, whicli, in most of the LEPT.a;NA, nearly fills the triangular foramen, 

 presents in this case a narrow channel or groove, leaving a passage for the extension of the 

 tendinous peduncle. The imperforate beak shows a distinct small point, projecting beyond 

 the cardinal line. The open foramen is probably due to the youth of the individual, as it 

 often happens that this passage becomes closed with age. Whether the perforation in the 

 beak may become developed as the shell advances in age, I am unable to determine. 



The specimens under consideration are apparently young shells, though I have not been 

 able to trace their gradation to the larger forms of L. alternata, or any other species. The 

 careful examination of six well preserved specimens shows a uniform development of the 

 characters above given. 



Fig. 10 a. Ventral valve of this species, showing the equal radiating striffi. 



Fig. 10 6. Dorsal valve, with unequal strise. 



Fig. 10 c. Cardinal area, and the same enlarged, showing the open foramen and imperforate beak. 



Position and locality. This shell occurs in the same situation and association with L. 

 alternata, L. sericea, and other species of the genus. 



There are, in addition to the foregoing, one or two undetermined or obscure species, 

 which require further investigation before they can be regarded as established. 



