LEDA DECUSSATA. 0~ 



Shell ovately triangular, inflated in front, behind attenuate, rostrate : ura- 

 bones nearly mesial, small, incurved, contiguous ; lunule sharply elliptical. 

 obscurely margined; area deeply excavated, bounded by a rounded, broad, 

 elevated ridge ; angle of hinge line obtuse : surface engraved with crowded 

 regular concentric stria? decussated by minute radial striae, and presenting a 

 beautiful appearance under the lens. 



Three specimens. Dimensions of that which is in best condition, and 

 figured: length, 12 mm.; height, 8 mm.; thickness, Gl mm. 



This species in form and superficial markings so closely resembles L. ve- 

 nusla Sauvage and Rigaux (Journal de Conchyliologie, XIX. p. 356, 1871 ; 

 XX, p. 180, PI. xi, fig. 7, 1872), from the Kimmeridgien mot/en de Brequerecques, 

 that in the outset I was strongly inclined to look upon it as a variety of 

 venusta. But on further examination it seems necessary to set it apart as a 

 distinct species, on account of the following differences. The French speci- 

 mens are smaller, their three dimensions being given respectively as 7. 4, and 

 3 mm. ; they have the anterior margin rounded, and the surface of the sides 

 radiatim costellata ct concentrice striata (op. cit., XIX, p. 356), or, ornie de cotes 

 rayonnanies nombreuses el de stries concentriques (op. cit., XX, p. 181). The Leba- 

 non shells, on the other hand, have their dimensions about twice greater than 

 those of venusta : viz. 12, 8, and 6^ mm. ; the front margin slopes in a nearly 

 straight line ; and the surface is engraved with close-set. well-impressed con- 

 centric stria?, crossed, not by costce nor costellce, but by radial striae so deli- 

 cate as to be visible only with aid of the lens. So also the Jurassic L. lacryma 

 Sow. sp., has very nearly the form of this species, but is distinguished from it 

 in being smaller, more prolonged posteriorly into a narrow rostrum, and in 

 having its surface marked with " concentric striations, rather remote, and 

 faintly impressed, sometimes undistinguishable " (Morris and Lycett, Mollusca 

 from Great Oolite, Part, II, p. 53, PI. v, figs. 15, 15 «, 1853). Coll. Bird. 



Locality mid Paxil ion. — Fraas records from the Ornati Clay of Mejdel esh 

 Shems, under the name of Nueula laeryma Sow. (Jahrbuch fur Mineralogie, 

 etc., 1877, p. 27, and A us dem Orient, II. Theil, p. 19, 1878), a, species which 

 in all probability is the one here described. The general similarity of the 

 two species has already been noticed above. One of our three specimens 

 has the test partly broken away, showing within a cast having the pyritif- 

 erous composition mentioned in connection with the species last described. 

 For reasons there and here stated, it is probable that these specimens of 

 Leda are from the Ornati Clay of Mejdel esh Shems. 



