268 Annals of the Carnegie Museum. 



Marsupium formed by the outer gills; when gravid moderately 

 swollen, with rather well-developed, leaf-like placentae. Glochidia 

 (see Ortmann, ignb, pi. 89, fig. 6) small, suboval, without hooks. 

 Length 0.13; height 0.15 mm. The color of the abdominal sac is 

 whitish, the foot pale gray or brownish gray, the mantle pale liver- 

 brown, whitish toward the margins, edge brown, black posteriorly. 

 Gills gray or dirty brown. Adductors whitish, palpi grayish. 



Elliptio beadleianus (Lea). 



Two males and two females, from Pearl River, Jackson, Hinds Co., 

 Mississippi, have been received from A. A. Hinkley. 



This species, which has been placed by Simpson (igoob, p. 786) 

 in the genus Quadrula, is not a Quadrula, because only the outer gills 

 have marsupial structure. In other respects its anatomy is indis- 

 tinguishable from that of other forms belonging in the genera of the 

 type of Pleurobema, etc. The shape of the gravid marsupium, of the 

 placenta?, and of the glochidia is unknown. 



The supra-anal opening is well separated from the anal, but the 

 separating mantle-connection is short. The inner edge of the anal 

 has fine, but distinct, papilla?, that ol the branchial has larger papilla?. 

 The posterior margins of the palpi are connected for one-third or one- 

 half of their length (this is the most prominent difference from the 

 allied forms). The inner lamina of the inner gills is free, as usual. 



Although the structure of the gills unquestionably removes this 

 species from Quadrula and Fusconaja, it is hard to assign it a place in 

 the other genera. We must rely entirely upon the shell, and this is 

 rather an indifferent criterion. However, I think the shape of the shell 

 is more like that of crassidens than that of any other form. It is some- 

 what more elongate than the Fusconaja- Pleurobema-type, straight, 

 with the beaks not much anterior, with a dark epidermis, and with 

 a tendency to develop red nacre, characters which are all found in 

 E. crassidens. The posterior ridge is also present in both species. 



I consider E. beadleianus a peculiar type, standing nearest to E. 

 crassidens. Probably other species go with it, as for instance chicka- 

 sawhensis Lea and askeici Marsh (of the latter two, Frierson writes 

 to me that they are "next to inseparable"). All these differ from 

 crassidens in being smaller, possessing more regularly swollen lateral 

 faces of the disk, lacking corrugations on the posterior slope, and having 

 a lighter nacre. Also the whole shell and the hinge are less massive in 

 structure. Their beak-sculpture is unknown. 



