Ortmann: Families vnd Genera oi Najades. 



233 



Haas omitted to saj anything aboul the gill-structure, his description 

 ol the margins of the mantle, of the diaphragm, and other parts renders 

 it absolutely certain thai this species musl be placed in the family 

 Margaritanida. Haas points oul certain differences from Mar- 

 garitana margaritifera, of which the mosl importanl is the fact that 

 the shell Ins lateral hinge-teeth. Since we have other genera among 

 the Najades in which the hinge-teeth arc variously developed, and 

 since it is absolutely clear, thai Margaritana margaritifera, withoul 

 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 importanl 

 characters are known to agree, while all the known differences .ire such 

 a- in other groups are known to be of minor value. 



Margaritana sinuata thus would represenl a somewhat more ancient 

 type than .1/. margaritifera (see Ortmann, 1911c, 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. 



■ t an 



Fig. 2. Margaritana monodonta (Say). Specimen from Cumberland River, 

 Rowena, Russell Co., Ky. (Cam. 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 

 teat tires 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. Xo supra-anal present. Posterior margins of palpi 

 connected for about one-third of their length, ('.ills rather long (cor- 

 responding to shape of shell), the inner the wider, chiefly so ante- 



