The Nautilus. 



Vol. XXVI. JUNE, 1912. No. 2 



CUMBERLANDIA, A NEW GENUS OF NAIADES. 



BY A. E. ORTMANN. 



Tlie type-species of this new genus is Unto monodonta of Say, 

 which stands, in Simpson's system (Pr. U. S. Miis. 22, 1900 p 679) 

 as Margaritana monodonta (Say). 



As Simpson lias correcitly recognized, this species has affinity with 

 the genus Margaritana (Type : margaritifera Linnaeus), and, con- 

 sequently belongs to my family Murgaritanida (Nautilus, 25, 1911 

 p. 129). Through the courtesy ot i\Ir. Bryant Walker 1 had the 

 opportunity to examine the soft parts of a number of individuals 

 from the Cumberland River, and was able to ascertain that all 

 essential cliaracters given by me for this family are present, chiefly 

 so the conformation of the diaphragm, of the posterior end of the 

 gills, and of the anal and branchial openings. But there is one 

 interesting difference. While in other species of the genus Margari- 

 tana the interlaminar connections of the gills are scattered, and 

 irregularly distributed, or fall into more or less distinct oblique rows, 

 in the present species these irregular, interrupted rows are devehped 

 as continuous septa, which run obliquely forwards. In the middle ot" 

 the gills, these septa are well developed and qiiiif continuous, but 

 rather distant from each other. Toward the ends of the gills they 

 are more irregular, shorti^r, and chiefly at the posterior end they are 

 somewhat interrupted, and thus it is clearly seen that tliey repres(Mit 

 a further development o\ the oblifjue, interrupted row-; |>re-fnt in other 

 species of Margaritana. 



The septa of this species {monodonta) have nothing to do with tlif 

 septa of the family Unionida. for in the latter tlw^y run parallel to 



