THE NAUTILUS. 17 



incased and slightly undulated at the tips ; ligament short and 

 thick ; epidermis brown ; rays obsolete ; cardinal tooth large, ele- 

 vated and widely cleft in the left valve and emerging from a pit in 

 the right valve ; lateral teeth thick and curved in a direction over 

 the cardinal tooth ; anterior and posterior cicatrices both distinct ; 

 dorsal cicatrices situated on the under part of the cardinal tooth ; 

 cavity of the beaks deep and angular ; nacre pearly white and iri- 

 descent. Length 2.3 ; alt. .2 ; diam. 1.5 in." 



It is to be noted that while this description is quite exactly in ac- 

 cord with the Ohio river species commonly called trigonus, the figure, 

 while its dimensions are those given in the description, is not in 

 strict accordance with its specifications nor with the shell as usually 

 found. The shell as figured (PI. II, fig. 1) would scarcely be 

 called " subtriangular," but rather subquadrate ; the beaks though 

 prominent are not characteristic of the shell as it actually occurs 

 and there is a decided emargination of the posterior slope, which is 

 not mentioned at all in the description, and which, so far as iny ex- 

 perience goes, does not occur in any form of trigonus. The figure, 

 as it stands, would do better for a representation of the not uncom- 

 mon quadrate form of rubigiuosus than of trigonus. 



It was probably on this account that the Western Academy of Nat- 

 ural Sciences, in their " Synopsis" of 1849, felt unable to determine 

 exactly what trigonus was and doubtfully referred it to JJavus Raf., 

 of which they considered rubiginosus an unquestionable synonym. 



Dr. Lea in his " Rectification " (Separate p. 6) speaks in the 

 highest terms of the judicial attitude maintained by the Academy in 

 the preparation of this list and of the impartiality with which they 

 attempted to " render strict justice to every author." 



It is to be noted in this connection that the figure of U. pyrami- 

 datus on Lea's plate is evidently exaggerated and out of propor- 

 tion and that of rubiginosus in the same volume is even more so. 

 It would therefore seem that the figure given cannot be confidently 

 relied upon as an accurate representation either of the species or of 

 the type. 



But, however that may be, there is no real question as to what Lea's 

 species is, although it does not appear to be a common one in the 

 Ohio River. I have myself seen only one specimen, that figured 

 (plate II, fig. 2). Of sixty specimens of the group recently submitted 

 by Dr. V. Sterki for examination from the Ohio at Marietta and 



