MODIOLOPSIS. 
41 
1. MoDioLOPsis LBPiDA, WMdbome, sp., PI. I, fig. 5. 
1889. Ctenodonta LEpiDA, ?F]^/i5orae. Geol. Mag., dec. 3, vol. vi, p. 79. 
Description. — Shell elongate, equivalve, flat, oblique, almond-shaped, very 
inequilateral. Umbo minute, proximate, direct, anterior, situate about one fourth 
the length of the shell from the anterior side. Hinge-margin straight, about 
half the length of the shell. Anterior margin narrow, very convex. Inferior 
margin oblique, slightly but evenly convex. Posterior margin straight and 
oblique in the upper part, and perpendicularly truncated in the lower part (this 
irregularity, however, being probably due to the fracture of the edges, and its 
true shape being an oblique slightly arched line, becoming very convex below). 
Hind wing rather concave. Pallial line simple. Anterior muscle-mark rather 
large. Shell-structure apparently very thin. 
8ize. — Length 20 mm., breadth 11 mm., depth 6 mm. 
Locality. — There is a single cast of the closed valves in the Museum of 
Practical Geology from Wolborough. 
Remarks. — The specimen here described is a cast in coarse saccharoid calcite, 
and hence its features are very indistinct. The characters of its hinge are 
obliterated, and the anterior muscular impression and the pallial line can only be 
made out with great difficulty. Consequently it is impossible to decide its genus, 
but its near resemblance to several Bohemian and other species of Modiolopsis 
renders it most probable that it belonged either to that genus or to Modiomorpha. 
Affinities. — It so closely resembles Modiolopsis tenera, Barrande,^ that it 
may possibly be a variety of that shell ; but it seems to differ in its front and rear 
margins being less blunt, and its umbo smaller and more direct. 
M. plebeia, Barrande,^ has a more elevated umbo and a rather shorter hinge- 
line, and is broader and shorter in front. 
Some of Hall's figures of Modiomorpha subalata, Conrad,^ var. Ghemungensisy 
Hall,* accurately agree with it, and so far might be identified, but there are signs 
that it was much deeper than our shell. Its muscle-mark, moreover, seems to be 
much smaller. 
From Pidlastra modiolaris, F. A. Romer,^ it is distinguished by its more central 
1 1881, Barrande, ' Syst. Sil. Boheme,' vol. vi, pi. celxxxv, figs. 1, 1-5, Et. E. 
2 Ibid., pi. cclviii, figs. 2, 1-7, Et. F. 
8 1841, Conrad, ' Geol. Surv. N. Y.,' Ann. Eept., p. 83. 
4 1885, Hall, ' Pal. N. Y.,' vol. v, pt. 1, sect. 2, p. 284, pi. xxxix, fig.. 15 ; and pi. xli, figs. 5—11. 
1850, F. A. Eomer, ' Beitr.,' pt. 1, p. 60, pi. ix, figs. 21 a, b. 
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