Ortmann: Families and Genera ov Najades. 357 



Truncilla haysiana (Lea). 



Four males, one su-rile, and one gravid female have been received 

 from B. Walker, they are from the Cumberland River in Ken- 

 tucky. 



Agrees in every particular with T. triquetra, with exception of the 

 inner edge of the mantle in front of the branchial in the female. Here 

 the papillae of the branchial are not markedly distant from the outer 

 edge, but in front of them the inner and outer edges of the mantle di- 

 verge considerably, both describing a short curve in opposite directions, 

 coming together again before they reach the middle of the ventral 

 margin. They enclose a lanceolate or broadly ovate space of spongy 

 structure and black-brown in color. The inner edge has four to six 

 distinct papillae in its anterior part, which are brown. Back of them, 

 toward the branchial, lies upon the edge a very remarkable, pure white 

 caruncle, which, in the alcoholic material at hand, is rounded, without 

 distinct shape or structure except a few crenulations. Inside of the 

 inner edge runs a black streak. The color of the mantle around the 

 branchial papillae and forward along the edge is dark black and brown, 

 and thus the caruncle is sharply marked off by its color. Anteriorly 

 the margin of the mantle is brown, and in the region of the anal and 

 supra-anal it is spotted with brown. In the male the two edges of 

 the mantle are very little distant from each other, the inner has small 

 papillae, one of which is pure white, but is much smaller than the 

 corresponding caruncle of the female. 



Marsupium more regularly kidney-shaped, than in T. triquetru. 

 Glochidia similar, but larger; length 0.24; height 0.23 mm. (see Plate 

 XX, fig. 11). 



Truncilla penita (Conrad). 

 This species, which, according to Walker (1910c, p. 77), belongs to 

 the triquetra-group, has been described by Lea (Obs., X, 1863, p. 440). 

 It has below the branchial "a small white fleshy mass ... of a sub- 

 sigmoid form, rounded at the bottom, and pointed at the top, and fur- 

 nished with some crenulations in the middle." There is no doubt 

 that this mass is similar and homologous to the white caruncle de- 

 scribed above in T. haysiana. I have not seen anything like it in 

 T. triquetra. But the presence of this organ, the function of which is 

 unknown to me, serves to connect more closely the two groups to which 

 T. triquetra and haysiana belong. 



