104 PALEONTOLOGY OF NEW-YORK. 
Fig. 1 2. This shell is a representative of that known as L. ponderosa in Ohio. In form it resembles the 
two preceding, 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 striz upon both valves resemble the preceding; but it often 
happens that those on the convex valve are more or less worn, so as to appear nearly equal. 
The character of the hinge, with the perforation in the beak, is the same in both varieties. 
This variety of form evidently consists of old shells, which often show marks of injuries 
that have been partially healed ; they also bear evidence of wearing, and are frequently 
covered with corals, from which the lighter and younger shell- is comparatively free. The 
view of the ventral valve and hinge line is precisely similar to the last; the lower figure is 
a lateral view, showing the great elevation of the dorsal valve and the abrupt curvature in 
front, with the strong imbricating lines of growth. 
Fig. 1k. An elongated form of this species; the dorsal valve showing the margin abruptly curved 
upwards from a little below the hinge line. The alternating strie are very perfectly re- 
presented, and the cardinal line presents the same characters as the previous ones; the 
foramen in this one being scarcely closed, while the minute perforation in the beak is very 
conspicuous. 
This form corresponds precisely with 1 f, while there is a little deviation in the alternation 
of the striz in that specimen. 
Fig. 1 m. The interior of the ventral valve, showing the visceral impression, and the two prominent 
toothlike processes between which the ligament of attachment passed out through the fora- 
men : these processes approach each other above, and produce the callosity, which, in most 
specimens, fills, partially or entirely, the foramen in the opposite valve. ‘I'he entire inner 
surface is papillose, and more strongly so on the visceral impression. 
Specimens of this kind, revealing the internal structure of the species, are of rare occur- 
rence in the Trenton limestone in New-York, though not unfrequently found farther west. 
ig. 1 m The convex valve of this species, with the shell partially exfoliated. The stronger radiating 
strie 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. 
Although presenting some slight deviations in the striz from the type of the L. alternata, 
I cannot find sufficient to characterize it as a distinct species. 
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Q 
Pirate XXXI. A. 
The elongated forms, figs. 1 f and k on the last plate, gradually assume a nasute shape, 
in which state they have been characterized as Strophomena nasuta by Mr. Conrap. The 
following illustrations will show sufficiently well how the species under consideration 
assumes this form. 
Fig. 1 a, A specimen which is contracted just below the ears and bent abruptly upwards, having towards 
the front several folds, and a more prominent one directly in front. 
Fig. 1 5. A lateral view of the same specimen, showing the abrupt and extreme deflection of the shell. 
Fig. 1 ¢. A specimen having the same general form as the last, but contracted and folded in front so as 
to present precisely the same form as the L. nasuta of Conran. 
