108 PALEONTOLOGY OF NEW-YORK. 



144. 7. LEPTiENA TENUISTRIATA. 



Pi.. XXXI. A. Figs. 4 a, b, c, d, e,f. 



Ref. Leptana ttnuiitriala. Sowerbt in Sil. Researches, pag. C30, pi. 23, 6g. 2 a. 

 Compare Z^pltma lieltoidea of Conrad ut supra. 



Semicircular, measuring the disc of tiie dorsal valve j liinge line extending beyond tlie 

 width of the shell, the extremities forming small acute ears ; dorsal valve with the disc flat, 

 abruptly deflected from the middle ; surface marked by about 9 or 10 (12, Sow.) concentric 

 wrinkles, which are crossed by numerous equal crowded striae ; cardinal area narrow linear ; 

 foramen nearly closed ; beak, in many instances, perforated. 



Fig. 4 a. A small specimen of this Shell, the dorsal valve having about four or five strong undulations 



upon the surface ; the cardinal extremities are strongly deflected. 

 Fig. 4 b. Cardinal line, showing imperfectly the deltoid foramen. 

 Fig. 4 c. A small specimen, having about six distinct undulations on the disc, and three less distinct ones 



towards the beak ; the shell bends abruptly upwards, nearly at right angles to the disc ; 



surface evenly marked by the radiating stria3 ; the extremities of the hinge line are acute 



and abruptly deflected, forming small ears. 

 Fig. 4 d. A small shell of this species, exhibiting very indistinct undulations upon the surface, being 



very abruptly deflected near the margin, and extremely extended on the cardinal line. 

 Fig. 4 e. A larger specimen, showing about four or five distinct undulations on the dorsal valve, and the 



same number on the ventral valve. The cardinal line is more extended than is usual in this 



species. 

 Fig. 4 / Ventral valve and cardinal line of the same species, showing the narrow almost linear area ; 



the latter enlarged, showing the perforation in the beak, which, however, may be due, in 



part, to injury. 

 Fig. 4 g. Lateral view of the same specimen, showing the abrupt deflection and elevation in front. 



This species of Mr. Sowerby, to which form ours bears a close analogy, is generally 

 regarded as identical with the Lepttena depressa ; but I am by no means satisfied that it is 

 not really different. In all the specimens which I have seen, the shell has a diflferent aspect, 

 is not so rounded, and is less regularly wrinkled. I have not been able to see the internal 

 structure, which will eventually decide the difference in the two shells. 



Should this prove to be the Lepttena rugosa, it establishes the existence of that species at 

 a much earlier period than we have been accustomed to suppose, and also that it is one of 

 those rare forms (and at present the only shell known to me) which reappeared after the 

 final deposition of the Hudson-river group. 



Position and locality. This species, though very rare in most localities where the other 

 forms of this genus are found, is sometimes seen in other associations near the higher part 

 of the limestone. It is unknown to me in the Hudson-river group, though at the west it is 

 found in a similar position. It occurs at Adams ( Jefferson county), near Turin ( Lewis 

 county) , and at Middleville. Among its western localities, Cincinnati and Oxford (Ohio) , 

 Maysville (Kentucky), and Madison (Indiana), are the most important. 



