LEPTODESMA. 121 



2. LEPTODESMA, sp. Plate XIV, fig. 1, and Plate XVII, fig. 1. 



Description. Left valve large, convex, extremely oblique and transverse. 

 Hinge-line straight, probably very much shorter than the length. Umbo small, 

 acute, very oblique, and situated at or close to the anterior end. Anterior wing 

 apparently very small, oblique and narrow, undefined. Posterior wing narrow, 

 flattish, triangular, with a thickened rounded upper margin over the hinge-line, 

 and apparently with a small rib or bead separating it from the body. Anterior 

 margin very long, oblique, and almost straight. Postero-inferior parts very 

 much produced. Contour of surface convex across the line from umbo to postero- 

 inferior corner, becoming steep near the anterior margin. Surface unknown, but 

 evidently having some growth-ridges which become concave on the hind wing. 



Size. A specimen, defective behind, is 27 mm. high and 40 mm. long. 



Localities. In the Barnstaple Athenaeum is a specimen from Pilton ; and in 

 Mr. Hamling's Collection another from the beach at Croyde. 



Remarks. Though these specimens are much too defective to enable us to 

 give a full description, they seem to point to a remarkable and very distinct species, 

 which (even allowing for possible distortion) was evidently characterised by its 

 oblique mytiliform shape, though it doubtless belongs to the present genus. 



Affinities. From Pterinea ventricosa, as given by Goldf uss, 1 Phillips, 2 

 Tollman/ and Freeh 4 (though the versions of these authors do not seem always to 

 agree with each other), it distinctly differs by its great obliquity and length, and 

 by the shape of its wings. 



From A. sublamellosa, F. A. Romer, 5 it is distinguished by its length, obliquity, 

 and short front wing. 



3. LEPTODESMA CDLTELLATUM, n. sp. Plate XIV, figs. 2, 2 a, 3. 



Description. Eight valve small, very elongate and oblique, sabre-shaped, 

 gently convex, with small defined wings. Umbo small, acute, prominent, hardly 

 elevated above the hinge, and situated at the anterior one-eighth of the shell. 

 Hinge-line short, straight, about half the length of the shell. Wings flat, 

 sharply defined by impressed bounding lines. Front wing small, long, 



1 1834-40, Goldfuss, ' Petref. Germ.,' vol. ii, p. 134, pi. cxix, fig. 2. 



2 1841, Phillips, ' Pal. Foss.,' p. 49, pi. xxii, fig. 82. 



3 1885, Follman, ' Verb. Nat. Vereins Eheinl.,' Jahr. 44, vol. xlii, p. 191, pi. v, fig. 7. 



4 1891, Freeh, Abhandl. Geol. Specialk. Preuss.,' Band ix, pt. 3, p. 97, pi. x, figs. 1 Ic. 



5 1850, F. A. Komer, ' Beitr. Harzgeb.,' pt. 1, p. 13, pi. iii, figs. 4, b. 



Q 



