Synopsis Frush-Water Moi,i,usca 



67 



Marsupium occupying the basal half of the entire length of the outer 

 gills and having in front six to twenty beautiful folds ; ovisacs distinct, each 

 ending below in an enlarged, rounded bulb, which has a colored spot in the 

 centre. 



7 an 



\br 



Type: Unio pJiaseolus Hild., fig. 187. Animal, P. subtentus (Say), fig. 188. 



Genus OBLIQUARIA Rafinesque, 1820. 



Shell inflated, solid, oval, ending in a tolerably sharp point behind, hav- 

 ing a row of large, compressed, longitudinal knobs running from the beaks 

 to the centre of the base, those of one valve alternating with the knobs of 

 the other, and a well developed posterior ridge, the space between the ridge 

 and the knobs somewhat excavated; posterior slope and sometimes the en- 

 tire shell more or less corrugately sculptured; beaks prominent, incurved 

 and pointed shghtly forward tOAvard a tolerably well developed lunule ; beak 

 sculpture strong, consisting of four or five heavy, parallel ridges, which fall 



.isa 



Fig. 189 



Fig. 190 



loAV in front, but are curved upwards behind ; epidermis smooth, generally 

 shining, painted with numerous, delicate, wavy, darker, broken rays; pseudo- 

 cardinals strong, distinct and ragged ; laterals short, nearly straight ; front 

 part of the shell very solid, suddenly becoming rather thin, just behind the 

 knobs. Marsupium consisting of a few, distinctly marked ovisacs (4 to 7) 

 occupying a position just behind the centre of the outer gills, projecting far 

 below the rest of the branchice, their bases rounded. 

 Type: 0. reilcxa Raf., fig. 189. Animal, fig. 190. 



