PLATE 31. 
1. 141. 4. Lept^na alternata. (Pag. 102.) 
1 a. A specimen of medium size, with the elevated striae very distinctly marked, and the gradual enlarging of 
one of the intermediate smaller striae is shown as they recede from the apex. 
1 b. A smaller specimen, presenting the characters of the species in a very perfect manner. 
1 b*. Enlarged portion of the surface. 
1 c. Inside of the dorsal valve of this species, showing imperfectly the visceral impression near the beak, and 
the papillose surface of the shell. The alternation of larger striae with fascicles of smaller ones is quite 
distinct. 
1 d. An individual of larger size, having the essential features of the species well preserved. This specimen is 
much more convex in the centre, and more abruptly curved in front, than either of the preceding. 
1 e . Dorsal valve of another specimen, in w 7 hich the length and breadth of the shell are about equal; and in 
this respect only does it differ from the preceding specimens, in which the width considerably exceeds 
the height. The larger and more elevated striae alternate precisely in the same manner with four to six 
smaller ones, the whole being crossed by fine concentric slightly undulating lines. 
1 /. A specimen having almost precisely the same form as 1 e ; but the larger striae are not so prominent, and 
the intermediate smaller ones not as regular as in the last specimen. 
1 g. The dorsal valve of this species, from the shaly blue limestone of Ohio. The surface is well preserved, 
and the striae very strongly marked : a few imbricating lines of growth are visible near where the cur¬ 
vature of the shell becomes abrupt. 
1 h. Ventral valve of another specimen : the radiating striae are nearly equal; the larger elevated ones, dividing 
the fascicles of small rays, being scarcely distinct, while on the dorsal valve they present the same 
distinction as in the last figure. The hinge view shows the deltoid foramen nearly closed, with the small 
perforation in the beak, which is enlarged in the upper figure. 
1 i. This shell is a representative of that known as L. ponderosa in Ohio. In form it resembles the two pre¬ 
ceding, except that it is more deflected on the margin, with more distinct imbricating and squamose 
lines of growth ; the space between the two valves is also much greater, and the shell more massive. 
The lower figure is of the dorsal valve, the two upper representing cardinal and lateral views. 
1 i*. Magnified view of a coral upon the shell. 
1 k. An elongated form of this species ; the dorsal valve showing the margin abruptly curved upwards from a 
little below the hinge line. The alternating striae are very perfectly represented; and the foramen is 
scarcely closed, while the minute perforation in the beak is very conspicuous. 
1 m. Interior of the dorsal valve, showing the visceral impression. 
1 in*. Enlarged portion of a coral which partially covers the interior of the shell, while the upper and left- 
hand margin is covered with Chcetetes lycoperdon. 
1 n. The convex valve of this species, with the shell partially exfoliated. The stronger radiating striae are very 
prominent, but the intermediate ones are obsolete except towards the hinge; the concentric elevated 
lines are, at the same time, very prominent. The shell is partially removed, so as to reveal somewhat of 
the internal structure. 
