266 PROCEEDINGS OF THE ACADEMY OF [Feb., 



La., and allied somewhat to rhomboidella Lea. It attained a length 

 of more than 20 mm., with a height of 12 mm. or more, obliquely 

 rhomboidal, moderately inequilateral, rounded anteriorly and posteri- 

 orly and broadly rounded ventrally. It is moderately inflated, the 

 radiating concavity at the middle of the umbones almost obsolete and 

 having merely shghtly wider intervals between the ribs, the latter 

 41-43 in number. The hinge-line is long and straight, the teeth becom- 

 ing larger and very oblique laterally but well developed throughout, 

 with their sides finely ribbed, giving to each tooth a bipectinate appear- 

 ance. The area under the beaks is ample and broadly, divaricately 

 striate. This species differs from rhomboidella in its much larger size, 

 more numerous ribs, rounded ventral edge and many other characters, 

 and may be named vaughani. A fair illustration of it was given by 

 Mr. Vaughan (Bull. Geol. Surv., 142, PI. Ill, fig. 8), in whose honor it 

 is named. A modification of the true rhomboidella, but still smaller in 

 size, also occurs sparingly at St. Maurice. 



SCAPHOPODA. 



Dentalium strenuum n. sp. 



In the Upper Vicksburg there are two large species of Dentalium; 

 one — jD. mississippiefise of Conrad — is moderately large, gradually 

 tapering throughout its length, feebly, evenly arcuate, having about 

 12 well-marked raised threads which l^ecome doubled or sometimes 

 quadrupled in number anteriorly, but generally almost effaced at the 

 mouth. A moderately large specimen measures 47 mm. in length by 4.6 

 mm. in maximum diameter. The other species, which may be named 

 strenuum,, is much larger, nearly straight, but becoming more rapidly 

 arcuate and also more distinctly tapering in form near the posterior 

 end. The ribs are some ten in number at the smaller end, becoming 

 generally quadrupled in number at the mouth, where they still remain 

 very distinct. The substance of the shell is much thicker, being fre- 

 quently 1.2 mm. through the walls near the middle. The notch at the 

 smaller end is nearly as in mississippiense, but generally deeper and 

 more acute. The largest entire specimen in my cabinet measures 67 

 mm. in length by 6.3 mm. in maximum diameter, but I have seen frag- 

 ments measuring more than 7 mm. in diameter and which represented 

 examples probably not much less than 90 mm. in length. 



Dentalium opaculum h. sp. 



Occurs in the; Lower Vicksburg in very great numbers. It is 

 smaller than mississippiense, somewhat less arcuate, gradually taper- 

 ing, notably uneven in growth and frequently more or less contorted at 



