540 



MEMOIRS OF THE CARNEGIE MUSEUM. 



lamellarly elevated (except indistinctly so near the margins), and the radial sculp- 

 ture is more distinct, consisting of faint furrows, becoming often subscalariform 

 toward the margins. 



3. The pseudocardinals of D. deceptus are more stumpy, chiefly in larger 

 specimens. In younger ones this difference is not so marked, yet noticeable, when 

 individuals of the same size are compared. In large specimens they are short 

 and thick, chiefly so the posterior one of the right valve, and the anterior of the 

 left (PI. XXXIX, figs. Ic, Id). The posterior one of the left valve generally is 

 well developed, although smaller than the anterior one. All these teeth are split 

 up into a number of denticles, and there are frequently accessory teeth, anteriorly 

 in the left, and posteriorly in the right valve. 



All other characters are as in D. gratus, but D. deceptus grows to a larger size. 



Measurements. 



Remarks. — In this species we also observe higher and more elongated shells, 

 nevertheless no relation between shape and sex is apparent. In fact, the most 

 elongated specimen No. 11, H. 65 pr. ct. (See PI. XXXIX, fig. 2) is a male, and not, 

 as might be expected (according to Von Ihering) a female. Altogether the number 

 of individuals with the sex positively known is rather small, but the gradual transi- 

 tion of the more elongated into the shorter and higher ones is evident. 



Anatoimj. — From Cachoeira, I have the soft parts of three young specimens, of 

 which the sex is not determined, and five males, and four barren females. 



Color of the distal part of the foot dark gray, this color sharply marked off 

 from the whitish basal part. The rest of the soft parts whitish. 



Anal Oldening closed above; the closed part about four times as long as the 

 open, which is slit-like, shorter (about three-fourths) than the branchial opening, 

 and separated from the latter by a solid mantle-connection. Branchial opening 

 short, with small, but distinct, papillae. Pali)i rather large, subtriangular, lower 

 margins strongly convex, posterior margins with a short connection at base. 



