116 FOSSIL ESTHERI^. 



ventral margin ; and the posterior space is based on the hinder margin, and reaches along 

 the dorsal region to the umbo. The surface of the valve is marked with 10-13 (?) delicate 

 ridges (hollow within), concentric, beginning at the umbo, conformable to the outline of the 

 valve, and sharply bent at the divergent ridges ; they are curved and closely set on the 

 anterior area ; more open, horizontal, and straight, or nearly so, on the middle area ; and 

 vertically straight or slightly curved, and wider apart, on the posterior part of the valve. 



These symmetrical markings of concentric angular lines and transverse divergent 

 ridges give this fossil, at first sight, a striking likeness to some Pish-scales, when the two 

 valves lie open, in contact by their dorsal edges (as in PL I, fig. 19), and produce a bilaterally 

 symmetrical, subquadrate, concentrically lined figure, with triangular sloping areas. 



Dr. Lea points out some Cyjpricardia and other shells of palaeozoic age to which this 

 little fossil has some resemblance in shape ; and some Orthonotce have a general resemblance 

 to it ; but some of the small Astaries of the Chalk and Oolite, such as the A. Boemeri, 

 Miiller's Petref. Aachen. Kreideform., PI. 6, fig. 12, and A. interlineata, Morris and 

 Lycett, MoUusca of the Great Ooolite (Palseontogr. Soc. Monograph), PI. 9, figs. 14, 15, 

 have even a greater resemblance in size and shape, without being at all allied to the form 

 before us. 



The horny tissue of Leaia, — its long dorsal edge, destitute of hinge, — its stiff and 

 simple style of ornament, — and its two diagonal, raised, hollow ridges or folds, remove it 

 from the MoUusca. It has been suggested (by Philhps and Williamson) that these fossils 

 may be Trigonellites (of Goniatites ?) ; but there is little or nothing to support the 

 hypothesis. 



Leaia Leidyi, Lea, sp. PL V, figs. 11, 12. 



Cypricaudia Leidyi, Lea. Proceed. Acad. Nat. Sc. Philadelphia, 1855, vii, p. 341. 



pi. 4. 



Height of valve, nearly -ox inch) _, ^. „ ^ ,„ , ,, 



^ -^ ^* [Proportion 7 to 12, or 1 : If — 



Length „ nearly /^ >, 3 



In the 'Proceedings Acad. Nat. Science of Philadelphia,' May, 1855, vol. vii, p. 341, 

 Dr. I. Lea has described a small fossil found by Dr. Leidy in a red sandstone at Tum- 

 bling Run Dam, about a mile south-east of Pottsville in Pennsylvania. The specimen con- 

 sists of the impression of the outside of the two valves. It is figured carefully, of natm^al 

 size, and enlarged, in plate 4 (op. cit.^), and is named Cypricardia Leidyi, by Dr. Lea, 

 who thus describes it : 



" Shell oblong, round before and truncate behind, very inequilateral, striate ; dorsal 

 and basal margins parallel ; umbonal slope shortly carinate ; anterior slope with an 



'^ By inadvertence, the enlarged view is stated to be magnified 10 instead of 5 times. 



