Ortmann: Families \m> Genera oj Naiades. 



315 



the outer walls ol the marsupium, around the edges of the placentae, 

 which arc central. Glochidia of peculiar shape, small, much longer 

 than high. 



Type D. dramas (Lea). 



This is a highly interesting genus, with several quite unique features 

 (general shape of marsupium, arrangement of glochidia and placenta?, 

 shape of glochidia), but there is no question that it belongs to the more 

 primitive types of the LampsilincE. In young specimens, where the 

 marsupium is not folded, the marsupium resembles somewhat that of 

 Obovaria, but without being so swollen. The general shape of the 

 shell, as well as the shape of the glochidia can only be compared with 

 that of Cyprogenia. I do not think that the folded marsupium in- 

 dicates closer relationship to Ptychobranchus, since here the folds are 

 of a different character. In the absence of special structures on the 

 edge of the mantle, this genus shows only a low stage of specialization, 

 without pointing to any particular affinity with other forms. 



Dromus dromas (Lea). 



I am indebted to B. Walker for seven complete specimens, and the 

 soft parts of nine others, all from the Cumberland River, in Pulaski, 

 Russell, Wayne, and Cumberland Cos., Kentucky. One of the soft 

 parts was a male, the others were all gravid females with glochidia. 



They all were collected late in 

 the season of 1910, so that the S3. 



beginning of the breeding season 

 is in autumn. 



The description of the marsu- 

 pium given by Simpson (19006, 

 p. 615) is entirely inadequate 

 and directly misleading, and in 

 one particular ("bases of the 

 ovisacs slightly rounded") un- 

 intelligible. 



Anal opening separated from 

 the supra-anal by a very short 

 and deciduous mantle-connec- 

 tion: only in two young and one 



older specimen was the latter preserved; but the others had been 

 rather roughly handled and the posterior region of the mantle was 



mp 



FlG. 18. Dromus dromas 1 ea 

 Gravid female, young (shell 41 mm. 

 long), from Cumberland River, Albany 

 Landing, Cumberland Co., Ky. (Cam. 

 Mus., No. 61, 4,970.) 



