234 BRITISH PALALZOZOIC FOSSILS. [Bracuiopopa. 
LEPTANA DELTOIDEA (Conrad.) 
Ref. and Syn.—Conrad, Geol. Rep. 1838. Hall, Pal. New York, t. 13 A. f. 3. > L. semi-ovalis (M°Coy), 
Sil. Foss. Irel. t. 3. f. 6. 
Sp. Ch.—Semioval ; hinge-line exceeding the width of the shell, forming short, convoluted, rounded ears; 
visceral disk obscurely defined, nearly semicircular, front narrow, rounded; receiving valve gently convex from 
the beak to the edge of the visceral disk, from which it is abruptly arched at an obtuse rounded angle, to 
form a deflected margin nearly as long as the visceral disk; cardinal area low, triangular, with a very wide, 
triangular, cicatrized foramen, and a small round aperture at the apex; surface of the visceral disk with 
more or less defined transverse wrinkles, usually nearly obsolete, but varying greatly in number, strength, and 
continuity, crossed by radiating, obtuse strixe, twelve to twenty, or commonly about fourteen in two lines, at 
four lines from the beak, rarely subequal or alternate, most usually with every third or fifth line larger than 
the others about the middle of the shell: internal cast of receiving valve striato-punctate, the triangular boss 
of the foramen having a small tubular papillate tubercle on the apex (corresponding with the external foramen 
at the point of the beak); two short cardinal teeth border the foramen, diverging at 90°, with long sub- 
parallel or slightly incurved dental lamellz, extending from their distal extremities from half to two-thirds 
the length of the visceral disk, enclosing the oblong pair of sulcated muscular impressions, which are 
nearly twice as long as wide. Width one inch five lines, proportional length of visceral disk {%, depth of 
deflected front =, depth of receiving valve =. 
This extremely variable species can scarcely be defined. Some of our Coniston specimens have scarcely 
a trace of transverse wrinkles, and have the profile gently arched from the beak to the length of the visceral 
disk, whence the front is rather more abruptly arched, the strive being equal on the sides, but every 3rd, 
5th, or 7th being larger than the rest on the middle of the shell, agreeing exactly with Hall’s figures 3a 
and 3d: to this variety it seems the L. complanata of Sowerby should be united. From these the passage 
is most gradual, in specimens from the same locality, to those with a more abruptly deflected front, less 
conyex visceral disk, and gradually developed more or less regular concentric wrinkles, agreeing with Hall’s 
figures 3¢ and 3, and his figures 4 of the same plate, which he refers to the ZL. tenwistriata of Sowerby ; 
from which all the varieties may be easily distinguished, by the narrow, rounded front giving the semi-oval 
instead of the rhombic outline to the disk, and the inequality of the strize, as well as the narrower, oblong 
muscular impressions, and the distinct tubular perforation of the beak, with its corresponding mamilla on 
the apex of the cast. This latter variety seems to include the still more strongly pronounced form which 
I have called ZL. semi-ovalis, and found very constant in its characters in the Bala limestone of Chair of 
Kildare, in Ireland. The different varieties of this species might be separated in the different subgenera 
Lepteena and Leptagonia, shewing these latter to be but sections of one genus, 
Position and Locality —Common in the Coniston (Bala) limestone of Coniston, Lancashire ; Bala limestone 
and sandstone of Alt yr Anker, Meifod, Montgomeryshire; not uncommon in the Caradoc sandstone of 
Horderly. 
Var. B. UNDATA (A/‘Coy). Pl. 1. H. fig. 38, 39. 
Ref. and Syn.=Orthis wndata (M°Coy), Silurian Foss. Irel. t. 3. f. 21. 
This apparently distinct shell is semioval, about one and half inches long, with a narrow deflected 
border rarely half an inch deep, the visceral disk gently convex, rugged, with twelve or fourteen very large 
undulating concentric wrinkles, sometimes much interrupted, and nearly obsolete (like the type I originally 
figured), crossed by radiating obtuse strixe, which vary singularly in size in the different specimens, alike 
in all other respects—one specimen haying only ten strive in two lines at four lines from the beak, and 
another having twenty-four, and many specimens haying the intermediate numbers: the lines are often 
subequal, or in all the middle portion towards the margin every 5th or 7th considerably larger than the 
rest. In the specimens I originally described the surface seemed smooth, except some faint traces which 
