40 DESCRIPTIONS OF 



^vithout rays; lines of growth numerous and distinct ; ligament very long and slender ; 

 unibonial slope slightly angular ; cardinal teeth rather large, erect, crenulate and 

 double in both valves; lateral teeth very long, rather compressed, curved and 

 enlarged at the posterior end ; anterior cicatrices deeply impressed and all three 

 distinct ; the posterior cicatrices distinct, the interior one being large and inflected, 

 the superior one being small and very much removed from the great one ; dorsal 

 cicatrices forming a long row across the cavity of the beaks ; pallial cicatrix rather 

 deeply impressed ; cavity of the shell deep in the left valve and shallow in the right ; 

 cavity of the beaks very shallow ; nacre silvery white. 



Remarks. — This very remarkable species of the Triquetra, of Klein, {Hyria, of 

 Lamarck,) was first placed in my hand by Tho. R. Ingalls, M. D., to whose kindness 

 I am indebted for many new species from rare and distant habitats. This specimen 

 consists only of the right valve, and was among shells received by Mr. Asa Fitch, 

 of Salem, New York, in a box from China, with Anodonta magnifica, Dlpsas plicatiis, 

 and other well known Chinese species. 



This is certainly the most remarkable form of any of the genus Triquetra yet 

 observed. Its remarkable transverseness at once removes it from suhviridis, Klein, 

 {avicidari'^, Lam.) In outline it approaches Spatha ccelesfis, (nobis.) It is the 

 first time that this genus has been observed out of South America, where it luis 

 heretofore been considered to be peculiar. The great posterior cicatrix is of an 

 unusual form, being irregularly elongate and but slightly oblique to the tooth above 

 it. The minor superior cicatrix is unusually distant from the posterior terminal point 

 of the lateral tooth, where it is usually placed in all the family Naiad&s. In this 

 shell it is removed quite half an inch from the point, and placed rather below the 

 tooth itself and nearly perpendicular to the end of the great cicatrix, which here is 

 obliquely directed towards the anierior instead of the posterior margin. Tho three 

 anterior cicatrices are remarkably distinct, the superior one being placed on the end 

 of the cardinal tooth. There is an appearance of a row of cicatrices under the dorsal 

 line, anterior to the great cicatrix, which is situated anteriorhj to the cardinal tooth. 

 The whole interior of the valve is covered with beautiful minute papillae. The beak 

 is so much eroded that it is impossible to say if the tips in a perfect state be undu- 

 late or not. 



In the short diagnosis which I made of this new species of Triquetra, (Proceedings, 

 vol. viii. p. 79,) I had but a single valve, which had the appeai'ance of being twisted 

 like Area tortvosa, Lin. This extraordinary form, which had never been suspected 

 to exist in any member of the family Naiades, excited great interest with the 

 Zoologists who saw it ; but it was still a matter of doubt whether the curve, although 

 exceedingly regular and presenting no appearance of constraint or injury, might not 

 be abnormal. This dou1?t has now. however. Ijeun put entirely at rtst. for the curve 



