68 THE NAUTILUS. 



of the mantle margin, passing gradually into the smooth 

 anterior section, of the edge. Posterior margins of the palpi 

 connected for about one-third or one-half of their length. 



Inner lamina of inner gills entirely connected with ab- 

 dominal sac. Marsupium kidney-shaped, consisting of many 

 ovisacs, located in the posterior section of the outer gill. 

 Glochidia celt-shaped, agreeing with the figure given by 

 Coker and Surber. Measurements length 0.09, height 0.18 

 mm. They are much smaller than those of P. alata (0.21 X 

 0.38), but about as large as those of P. laevissima (0.12 X 

 0.18), but the latter are more dilated at the lower margin. 



Soft parts whitish throughout, with the mantle margin 

 brownish-black, more intensely so posteriorly. 



Nobody, except Coker and Surber, has doubted hitherto, 

 that this species, according to the shape of the shell, is closely 

 allied to Lampsilis ovata and ventricosa, in fact, the shape 

 of the shell is very much like that of old females of L. ventri- 

 cosa. Anatomical investigations has shown now, that this is 

 no Lampsilis at all. It is a true Proptera, and a close exam- 

 ination of the shell reveals, that the resemblance to L. ven- 

 tricosa is indeed only superficial. This is shown first of all 

 in the character of the hinge teeth, of the ligament and the 

 symphynote character of the upper margin, and then by the 

 lack of a distinct differentiation of the male and female 

 shell. In the female, the postbasal region is indeed slightly 

 expanded ; but this difference is very indistinct, in fact, I was 

 unable to tell the males from the females, before I had looked 

 at the soft parts: the sexes are even less distinct than in 

 the other species of Proptera. 



The present specimens show that glochidia are present at 

 the beginning of August and the beginning of October, but 

 they do not give an indication as to the duration of the 

 breeding season. 



Genus: CARUNCULINA Simpson, 1898 (as subgenus, Simpson, 

 1900, p. 563, and Ortmann, 1912, p. 337). 



I think now, that Carunculina is entitled to generic rank. 

 Characters of the shell (chiefly the beak sculpture), and 



