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 (Rossmessler). 
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. Israél. 
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.)” 
Simpson, 1900), p. 840.—Ortmann, 1910), p. 139. 
Shell subovate or subquadrate, with rather high beaks, moderately 
deep 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 thanin theinner. 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. 
Placentze 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 Fusconaja-sculpture. Some minor 
features of the soft parts indicate that it has advanced a little along its 
* Determined only by the type-species, mullidentata Philippi =corrugatu Mueller 
(see Conrad, 1853, p. 267). The investigated species, wynegungaénsis Lea is closely 
allied to the type. 
