32 



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

 N. N. Flem. Brit. An., p. 401. Kot uncommon. 



N ATA DA. 



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 lis 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. M ARGARITIFERA, My a M. Turt. Lin. Pen. Brit. 



Zo., vol. 4, pi. 43, fig. 13. Mont. Test. Brit., vol. 1, p. 33. 

 Alasmodon M. Flem. Brit. An., p. 417. Grays Turt., 

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

 larger rivers, as the Camel and Tamar. 



CONCHIFE R A UNIMUSCULQSA. 

 With one muscular impression, nearly in the middle of 

 the interior. 



MY TIL ACE A. 



The Ligament at the hinge subinterna!, marginal, linear, 

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

 rarely foliated. 



MODIOLA. 



GENERIC CHARACTER: Shell suhtransverse, 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. Muilus Modiolus. Turt. Lin. Pen. 

 Brit. Zo., vol. 4, pi. 66, tig. 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 

 from 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 dravsn up it was attached to a bed of fine gravel re- 

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



