78 OBSERVATIONS ON NAIADES, 



My Cabinet. 

 Diam. -9, Length 1-5, Breadth 1-6 inches. 



Shell triangular, nearly equilateral, very angular behind, and round- 

 ed before ; anterior portion furnished with triangular formed tuber- 

 cles, the apices of which point to basal margin ; portion immediately be- 

 fore umbonial slope free from tubercles ; umbonial slope elevated and 

 tuberculated from the beaks to the margin ; posterior slope truncate, 

 undulated, nearly perpendicular, flat, with the exception of a small 

 portion of the margin behind the ligament ; umbones flattened ; sub- 

 stance of the shell thick ; beaks prominent ; ligament short and thick ; 

 epidermis yellow, slightly wrinkled, and furnished with indistinct, 

 small, green pencil marks in the place of rays; cardinal tooth rather 

 large, elevated and widely cleft in the left valve, single and emerging 

 from a pit in the right valve ; lateral teeth very short, straight and 

 pointing to the basal margin ; the cardinal and lateral teeth are sepa- 

 rated by a flat plate ; posterior and anterior cicatrices both distinct, 

 the smaller posterior one being placed directly over the larger, and be- 

 neath the point of the lateral tooth ; dorsal cicatrices situated on the 

 under part of the cardinal tooth ; cavity of the beaks deep and angula- 

 ted ; nacre very pearly and iridescent. 



Remarks. — This very curious and interesting shell was among the 

 many fine specimens sent me by Judge Tait, to whose kindness I am 

 under great obligations for several of the new species here described. 

 The present species, in outline, is an anomaly in the family Naiades. 

 The truncature behind is almost as abrupt as that of any Donax. 

 This truncature gives the shell the form of a stirrup, and causes the 

 lateral teeth to take a direction (towards the basal margin) peculiar to 

 this species. The triangular form of the tubercles, particularly on the 

 superior anterior part, is so peculiar as to render it impossible to confound 

 it with any other species. 



