ORTMANN: FAMILIES AND GENERA OF NAJADES. 233 
Haas omitted to say anything about the gill-structure, his description 
of the margins of the mantle, of the diaphragm, and other parts renders 
it absolutely certain that this species must be placed in the family 
Margaritanide. Haas points out certain differences from Mar- 
garitana margaritifera, of which the most important is the fact that 
the shell has lateral hinge-teeth. Since we have other genera among 
the Najades in which the hinge-teeth are variously developed, and 
since it is absolutely clear, that Margaritana margaritifera, without 
lateral teeth, must have descended from forms with such teeth, I 
think the differences in Unio sinuatus should be regarded as only of 
specific value, and I see no reason why we should not place it with 
Margaritana, with which some of its most essential and important 
characters are known to agree, while all the known differences are such 
as in other groups are known to be of minor value. 
Margaritana sinuata thus would represent a somewhat more ancient 
type than M. margaritifera (see Ortmann, I9II¢, p. 6). 
Margaritana monodonta (Say). 
I have received, from B. Walker, one complete specimen, and the 
soft parts of three others, all from the Cumberland River in Pulaski, 
Russell, and Cumberland Counties, Kentucky. 
Fic. 2. Margaritana monodonta (Say). Specimen from Cumberland River, 
Rowena, Russell Co., Ky. (Carn. Mus., No. 61, 4,960.) 
We may compare the description of the soft parts by Lea (Obs., X, 
1863, p. 422), which, however, mentions among the important 
features only the posterior end of the gills, the branchial and anal 
openings. 
Margins of the mantle, branchial and anal openings as in M. mar- 
garitifera. No supra-anal present. Posterior margins of palpi 
connected for about one-third of their length. Gills rather long (cor- 
responding to shape of shell), the inner the wider, chiefly so ante- 
