172 PROCEEDINGS OF THE GEOLOGICAL SociETy.  [ Dec. 1, 
dantly in the Hamilton group of New York and in the Ludlow 
formation of Westmoreland. 
(3) AvicULA NAvIFORMIS, Conrad.—‘‘ Lower valve subrhom- 
boidal, slightly ventricose, obscurely radiated ; summit of umbo much 
above the cardinal lme; anterior wing triangular; posterior wing 
elongated ; angulated at the extremity, which extends beyond the le 
of the posterior extremity of the valve; umbonal slope rounded, not 
suddenly depressed, except on the umbo*.” 
Perhaps this shell may be only a variety of 4. retrofleca of 
Hisinger, to which it is closely allied. It is one of the commonest 
forms of this genus in the Ludlow rocks of Westmoreland, and is 
found in New York in the Pentamerus limestone at Schoharie. 
(4) AvicuLa quapRULA, Conrad.—“‘ Subquadrate, length and 
breadth equal, compressed ; lower valve plano-convex, with Gietiees . 
radii of equal size crossed by concentric lines ; posterior wing rather 
shorter than the width of the shell ; anterior wing triangular, beneath 
which the margin is direct before rounding to the base.” 
This is closely allied to A. Boydzi, but is thinner and flatter: per- 
haps they may be only varieties of one species. 4. emaceratat can- 
not be separated from this. 
From the Hamilton group of Nee York and Ludlow formation of 
Westmoreland. 
(5) Lepta#na pemissa, Conrad sp.——‘‘ Length and width nearly 
equal; inferior valve ventricose ; superior valve deeply concave ; 
radii sharp, prominent, subtuberculated, much more prominent on 
the upper than on the lower half of the valves, where they greatly 
bifurcate and become fine and very numerous; umbo convex, the 
summit slightly elevated ; hinge-angles slightly salient § Mi 
The specimens of this Enel are not perfect, but as far as can be 
seen they have no trace of any foramen whatever. The convex or 
dorsal valve has a rather broad hinge-area strongly marked by lines 
parallel to the hinge which continue without interruption along the 
whole area: the ventral valve has a narrower area which is also con- 
tinuous. Both areas are also striated in a direction perpendicular to 
the hinge. 
The absence of any foramen at the hinge i is very rare among the 
Brachiopoda and deserves particular notice. It will probably be found 
to indicate a distinct genus, as it must be accompanied with a peculiar 
internal arrangement. Until this can be ascertained this species may 
remain in Leptena, the genus to which it is most nearly related. 
(6) Leptena depressa. Many well-preserved specimens of this shell, 
from the blue limestone and the Niagara shale, have a circular foramen 
in the beak of the dorsal valve, just above the point of the triangular 
deltidium. I find a similar foramen in some young specimens of the 
same species from the Wenlock shale of this country : and on several 
old specimens a trace of such an opening may be seen on the outside 
* Conrad, Journ. Acad. Nat. Sci. Phil. vol. viii. p. 240, and t. 122 a1e 
+ Conrad, loc. cit. p. 243, and t. 13. f. 5. 
+ Conrad, loc. cit. t. 12. f. 15. 
§ Conrad, loc. cit. p. 258. 
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