UNIONIDJE. 295 



much and extensively eroded belong to the other 

 variety ; and the extent of the inflection generally 

 agrees with the state of the umbo. Figure 9. repre- 

 sents the intermediate state between the two varieties, 

 and figure 10. much more resembles a younger speci- 

 men, both in form and colour, than any English Umo 

 I have ever seen. 



3. UNIO Retz. (Union.) 



Shell oblong-elongate ; hinge with a short, crested, 

 irregular, anterior, and an elongated, laminar, pos- 

 terior, lateral tooth, in the right valve, shutting 

 between two similar teeth in the other valve. 



Lives in slow rivers and streams. 



These shells are liable to distortion about the 

 hinge ; the margin becomes thinner and extended ; 

 the shell truncated in front, the lunule enlarged and 

 irregular, and the teeth nearly obliterated. It gives 

 a wedge-shaped appearance to the shell. 



* Anterior teeth compressed, elevated, sometimes crested. 



124.1. UNIO pictorum. Thin Painter's Union, (t. 2. 

 f. 11.) Shell oval-oblong, ventricose, produced 

 into a bluntly truncated beak behind, yellowish 

 green, brownish zoned, greenish behind; upper 

 edge nearly straight, lower rather retuse ; hinge 

 teeth very much compressed, arched, crenated ; 

 hinder teeth of left valve small or evanescent. 



Young shell with a few isolated conical tubercles 

 on the umbo. Pfeiffer, ii. t. 2. f. 24. 



Mya pictorum. Linn. S. Nat. ? ; Sturm, Fauna, 

 vi. 2. f. a.; Wood, Conch. 104. t. 19. f. 3,4. 

 Schroet. Flussc. t. 4. f. 6. 

 o 4 



