32 
* N. NUCLEA. Area N. Mont. Test. Brit., vol. 1, p. U*' 
N. N. Flem. Brit. An., p. 401. Not uncommon. 
IS MAD A. 
Fresh Water Shells; the hinge with an irregular, simp' 0 
or divided cardinal tooth, and a longitudinal one, whic 1 
extends under the corselet; sometimes no tooth; or w|t J 
irregular granular tubercles through its length. Muscula 
impression posterior, compound ; the beaks decorticated 0 
eroded. 
UNIO, 
GENERIC CHARACTER: The shell transverse, wf 1 ’ 
equal valves, unequal sides, free ; beaks decorticate) 
almost eroded ; muscular impression posterior, compound > 
hinge with two teeth in each valve; one cardinal, shot) 
irregular, simple, or divided into two suhstrialed ; the otl> er 
elongated, compressed, lateral, prolonged under the cors e 
let. Ligament external. 
* U.MARGARITIFEliA. Mya M. Turt. Lin. Pen. Bf" 
Zo., vol. 4, pi. 43, fig. 18. Mont. Test. Brit., vol 1, p- s f‘ 
Alasmodon M. Flem. Brit. An., p. 417. Gray’s 1 ur 
p. 293, pi. 2, fig. 9. River Muscle. In some of ° u 
larger rivers, as the Camel and Tamar. 
CONCH1FERA UNIMUSCULOSA. f 
With one muscnlar impression, nearly in the middle 0 
the interior. 
MYTILACEA. 
The Ligament at the hinge subinternal, marginal, line 3 *"’ 
verv entire, occupying a great part of the anterior marg 111 ’ 
rarely foliated. 
MODIOLA. 
GENERIC CHARACTER : Shell subtransverse, 
equal valves, regular, the posterior side very short: be* 
nearly lateral, depressed on the short side ; hinge toot ^ 
less, lateral, linear. Ligament cardinal, almost intern* ’ 
in a marginal canal ; one sublateral muscular impressi® 
lengthened, axeshaped. n 
* M. VULGARIS. Mvtilus Modiolus. Turt. Lin. 
Brit. Zo., vol. 4, pi. 06, fig. 77. Mont. Test. Brit., vol ’ 
p. 163. M. V. Flem Brit. An., p. 412. Scarcely c0l i( j 
mon, and I have never obtained it of the size rnenli° n ' ;|1 
by Pennant and Montagu. The description of a speci" 1 ^ 
from deep water, differs so greatly from theirs, as a)i° ^ 
to suggest the suspicion of a different species. The le ° 0 |y 
was an inch and half, the substance thin and appare° 
brittle; the surface smooth, with no perceptible ej>id® rn 
When drawn up it was attached to a bed of fine- grave ,( 
dining on a stone; and having been taken with a book* 
