276 Annals of the Carnegie Museum. 



right outer gill filled with eggs. There were also eggs in the supra- 

 branchial canal. No glochidia were seen. The water-tubes had no 

 lateral water-tubes developed. 



Unio crassus consentaneus (Rossmsessler). 



A male from the drainage of the Danube in Bavaria, and three 

 males and four females from the Danube in Hungary, were sent to me 

 by W. Israel. 



Agrees in all particulars with the foregoing forms. (A cross-section 

 of the gills of the female is seen on Plate XVIII, fig. 5.) 



Genus Parreysia Conrad. (1853.) 22 

 Simpson, 1900&, p. 840. — Ortmann, 1910b, p. 139. 



Shell subovate or subquadrate, with rather high beaks, moderately 

 deop beak-cavities, and well developed hinge-teeth. Epidermis 

 bright, sometimes rayed. Beak-sculpture of the radial type: two sets 

 of radial ridges run from in front and from behind the beaks in the 

 direction of the lower margin. The two sets of radial ridges meet in 

 the middle of the shell in an acute angle, and sometimes extend well 

 upon the disk. 



Soft parts partly primitive, partly more advanced. Supra-anal 

 separated from the anal by a well developed mantle-connection, which 

 is rather long. Inner lamina of inner gills entirely connected with the 

 abdominal sac. All four gills are marsupial in the female, with well 

 developed septa and water-tubes, which latter are somewhat narrower 

 in the outer gill than in the inner. In the male, the septa are distinctly 

 more distant than in the female. During pregnancy, the gills swell 

 but little, and the edges remain sharp, and the ovisacs remain simple. 



Placentae subcylindrical, only slightly compressed, and not very 

 solid. Glochidia not observed. 



This genus, in the structure of the soft parts, corresponds to Fus- 

 conaja, Crenodonta, and Quadrula, to which it is apparently related, 

 but represents another type of development of beak-sculpture, which 

 may be derived from the simple F/z-srcwflja-sculpture. Some minor 

 features of the soft parts indicate that it has advanced a little along its 



22 Determined only by the type-species, multidentata Philippi =corrugata Mueller 

 (see Conrad, 1853, p. 267). The investigated species, wynegungaensis Lea is closely 

 allied to the type. 



