116 PALEONTOLOGY OF NEW-YORK. 
154. 17. LEPTASNA —— ( Species undetermined ) . 
PL. XXXI. B. Figs. 10 a, b, ¢. 
Semioval ; greatest width 12, height ;5 of an inch ; cardinal line scarcely equalling the 
greatest width of the shell below ; surface moivicea by fine radiating strize, which are crossed 
by fine concentric lines ; striz 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 the 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 
no more than might be expected between the young and old individual. The callosity of 
the ventral valve, which, in most of the Leprana, 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 prebably 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 strie. 
Fig. 10 4. Dorsal valve, with unequal strie. 
Fig. 10 c. Cardinal area, and the same enlarged, showing the open foramen and perorats beak. 
Position and locality. This shel! 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. 
