75 



marks that the "young shells are almost yellow, and 

 the animal of a deep or orange-yellow colour," which 

 accords with my own observation. I do not, how- 

 ever, consider the colour of the animal any safe guide 

 in specific distinction, as I have found the same spe- 

 cies, particularly V. decisus, to contain in some spe- 

 cimens an orange coloured, and in others a perfectly 

 white animal. 



UNIO CAPAX. 



Plate XLII. 



DESCRIPTION. 



Shell very globose; valves rather thin, translucent, 

 connate; umboncs tumid, summit obtusely rounded, 

 prominent, distant from the anterior margin; epider- 

 mis straw colour, polished, with two faint green rays 

 on the posterior slope; within white and iridescent; 

 cardinal teeth lamellar, prominent, double in the right 

 valve, crenate and single in the left; lateral teeth 

 arcuate. 



SYNONYMES. 



U. capax, Green. Cab. of Nat. Hist, vol. ii. p. 290. 1832. 

 Symphynota globosa, Lea. Trans. Amer.Phil. Soc, new series, 



vol. iv. p. 153, pi. iv. fig. 12. 1834. 

 Cab. A. N. S. No. 1227. 



OBSERVATIONS. 



The most ventricose of all the Unios known, and, 

 when young, one of the most delicate and beautiful. 



