32 



* N. NUCLEA, Area N. Mont. Test. Brit., vol. 1, p. 141. 

 N. N. Flem, Brit. An., p. 401. Not uncommon. 



NAIAD A. 



Fresh Water Shells ; the hinge with an irregular, simple 

 or divided cardinal tooth, and a longitudinal one, which 

 extends under the corselet; sometimes no tooth; or with 

 irregular granular tubercles through its length. Muscular 

 impression posterior, compound ; the beaks decorticated or 

 eroded. 



UNIO, 

 GENERIC CHARACTER: The shell transverse, with 

 equal valves, unequal sides, free ; beaks decorticate, 

 almost eroded ; muscular impression posterior, compound ; 

 hinge with two teeth in each valve; one cardinal, short, 

 irregular, simple, or divided into two substriated ; the other 

 elongated, compressed, lateral, prolonged under the corse- 

 let. Ligament external. 

 *U.MARGARITIFERA. Mya M. Turt. Lin. Pen. Brit. 

 Zo., vol. 4, pi. 43, fig. 18. Mont. Test. Brit., vol. 1, p. 33. 

 Alasmodon M. Flem. Brit. An., p. 417. Gray's Turt., 

 p. 293, pi. 2, fig. 9. River Muscle. In some of our 

 larger rivers, as the Camel and Tamar. 



CONCHIFERA UNIMUSCULOSA. 



With one muscnlar impression, nearly in the middle of 



the interior. 



MY TIL ACE A. 

 The Ligament at the hinge subinternal, marginal, linear, 



very entire, occupying a great part of the anterior margin ; 



rarely foliated. 



MODIOLA. 



GENERIC CHARACTER: Shell subtransverse, with 

 equal valves, regular, the posterior side very short : beaks 

 nearly lateral, depressed on the short side; hinge tooth- 

 less, lateral, linear. Ligament cardinal, almost internal, 

 in a marginal canal ; one sublateral muscular impression, 

 lengthened, axeshaped. 



* M. VULGARIS. Mvtilus Modiolus. Turt. Lin. Pen. 

 Brit. Zo., vol. 4, pi. 66, fig. 77. Mont. Test. Brit., vol. 1, 

 p. 163. M. V. Flem Brit. An., p. 412. Scarcely com- 

 mon, and I have never obtained it of the size mentioned 

 by Pennant and Montagu. The description of a specimen 

 irom deep water, differs so greatly from theirs, as almost 

 to suggest the suspicion of a different species. The length 

 was an inch and half, the substance thin and apparently 

 brittle; the surface smooth, with no perceptible epidermis. 

 When drawn up it was attached to a bed of fine gravel re- 

 clining on a stone; and having been taken with a hook, it 



