Unio. MOLLUSCA. UNIONISE. 417 



marked by lines of growth ; hinge strong Sower. Min. Conch, t. clxxxv. — 



In Crag. 



8. U. Solandrii — Transversely oblong-ovate, slightly arched, rather com- 

 pressed, thin ; both extremities obtuse ; beaks small, rugose, hinge slender. 

 — (Mya Pictorum, Brander, Foss. 105.) Sower. Min. Conch, t. Dxvii. — In 

 Crag. 



9. U. concinnus — Transversely oblong, ovate, depressed, nearly smooth, 

 thick ; posterior side very small ; beaks prominent, recurved — Sower. Min. 

 Conch, t. ccxxiii. — Inferior Oolite. 



10. U. Urii. — Transversely oblong, dorsal margin nearly straight ; une- 

 qually striated by the lines of growth — Muscle, Ure, Hist. Ruth. 311. 

 t. xvi. f. 4. — Mya ovalis, Mart. Derb. t. xxvii. f. 1, 2. — In Slate Clay of the 

 Coal Formation. 



Gen. CVIII. ALASMODON.— Shell transverse, hinge with 

 a single tooth in the right valve, recurved into a divided 

 tooth in the left ; no lateral teeth. 



429. A. margarit'if'erum. — Ventral margin slightly concave ; 



shell, towards the ligamental margin, compressed. 



Musculus niger. List. Conch, t. cxlix — Mva margaritifera, Linn. Syst- 

 i. 1112. Mont. Test. Brit. 33 — Unio marg. Turt. Biv. Brit. 249- 

 t. xvi. f. 1 — In gravel in rapid streams. 



Length about 2, breadth upwards of 4 inches ; cuticle brownish black ; 

 beaks worn, shell thick ; the lines of growth fine ; inside pearly. Pearls are 

 frequently met with in this species. 



CARDITAD.E. 



Gen. CARDITA.— Shell inequilateral ; hinge with two teeth, 

 the shortest beneath the beaks, the other oblique and mar- 

 ginal beneath the insertion of the cartilage. 



1. C. striata — Quadrangular, gibbous; the beaks placed at one of the an- 

 gles ; obliquely striated from the beaks to the edge. — Sower. Min. Conch, 

 t. lxxxix. f. 1 — Liferior Oolite. 



2. C. abrupta — Triangular gibbous, beaks projecting near one angle ; ob- 

 liquely striated ; anterior side longitudinally striated ; five or six transverse 



reflected ridges along the front — Sower. Min. Conch, t lxxxix. f. 2 Inferior 



Oolite. 



3. C. luberculata — Heart-shaped, longitudinally radiated, radii tuberculat- 

 ed ; valves equal, laterally compressed, longitudinally subcarinate, one side 



semilobate, the other nearly flat, beaks much incurved Sower. Min. Conch. 



t. cxliii. In Green Sand. 



4. C. lunulata — Rhomboidal, pointed, gibbose, transversely costated ; an- 

 terior part separated by a projecting serrated keel, lunette deeply excavated ; 

 beaks involute. Sower. Min. Conch, t. cexxxii. f. 1, 2. Inferior Oolite. 



VOL. I. ])d 



