416 
MOLLUSCA. UNIONID^. 
Unio. 
Gen. evil. UNIO. — Shell transverse; hinge with an ob- 
lique crenate tooth ; an elongated laminal tooth under the 
ligament in one valve received into a groove in the other. 
426. U. pictorum. — Ventral margin of the shell slightly in- 
curved ; hinge-tooth of the left valve nearly entire. 
Musculus angustius, List. Conch, t. cvxii. f. 3 — Mya pict. Linn. Syst. i. 
1112. Mont. Test. Brit. 36. — Mya ovalis and M. depressa, Don. Brit. 
Shells, t. Ixxxix. and ci. — Mysca ovata, Turt. Biv. Brit. 246.— Bivers 
in England. 
Length 1 4, breadth 3 inches ; cuticle green, dusky along the layers of 
growth ; posterior extremity slightly compressed, and obliquely truncated. 
427. U. ovalis. — Ventral margin slightly rounded; hinge- 
tooth of the left valve divided. 
Mytilus angustior. List. An. Ang. 149. Conch, t, cxlvii. 2. — M. ovata, 
Don. Brit. Shells, t. exxii.— M. ovalis, Mont. Test. Brit. 34 Mysca 
pictorum and M. solida, Turt. Biv. Brit. 245 — llivers in England. 
Nearly of the same dimensions as the last ; cuticle dusky or green ; more 
tumid, and rounded anteally, than the last. 
428. M. Batava. — Shell wide, with both extremities nearly 
equally rounded. 
M. pictorum, Don. Brit. Shells, t. clxxiv. — Mysca batava, Turt. Biv. 
Brit. 244. — In rivers, Oxfordshire. 
Length 1 inch, breadth 2 inches ; greenish brown ; thin ; the primary tooth 
of the left valve deeply divided. 
EXTINCT SPECIES. 
1. U. subconstrictus — About twice as broad as long, with a constriction 
running from the front of the shell towards the beak on the posterior side, 
the end of which is subtruncated — Sower. Min. Conch, t. xxxiii. f. 1, 2, 3. — 
In Ironstone in the Coal formation. 
2. U. uniformis — Subovate, beak near the middle of the shell ; both ends 
elliptical Sower. Min. Conch, t. xxxiii. f. 4 — Middle Oolite. 
3. U. acutus. — Anterior side acute ; twice as wide as the other, which is 
blunt or rounded. Width two and a half times its length.— Min. 
Conch, t. xxxiii. f. 5, 6, 7* — Middle Oolite. 
4. U, crassissimus Ovate, transversely undulated or imbricated ; beak re- 
curved, acute ; posterior side short, round ; anterior side obscurely subcunei- 
form; shell very thick.— Min. Conch, t. cliii. — In Lias. 
5. U. Listeri — Cordate, transversely imbricated, beak recurved, acute ; 
posterior side small ; middle flattish ; shell thick. — Sower. Min. Conch, 
t. cliv. f. 1, 3, 4. — Inferior Oolite. 
6. U. hyhrida Oblong, ovate, anterior side subacuminate ; surface im- 
bricated ; beaks recurved, acute ; shell thick. — Sower. Min. Conch, t. cliv. 
f. 2. — Magnesian Limestone. 
