FAMILY MYTILIDZ — MYTILUS. 181 
N. tenuis. (Gourp, l.c. p. 105, pl. 54.) Shell small, thin, trapezoidal, smooth, without radiating 
lines: beaks prominent, placed anteriorly; margin simple. Teeth long and slender, about eight 
behind and four or five before the beaks. Color : epidermis grass-green. Length, 025 ; transverse 
diameter, 0°3. Stomachs of fishes. 
N. minuta. (Goutp, |. c. p. 101. MN. tenuisulcata, Couruovy, Bost. Jour. Vol. 2, p. 64, pl. 3, 
fig. 8. Px. 12, fig. 213 of this book.)- Shell ovate, lanceolate, inequilateral, posteriorly much 
narrowed and rostrated: surface with numerous concentric ridges. Teeth twelve before and sixteen 
behind the beaks. Color: epidermis light greenish yellow. Length, 0+9; transverse diameter, 
1-0. Stomachs of fishes. 
NN, acuta. (Conran, Mar. Conchol. pl. 6, fig. 2.) Shell very small, ovate-elongate, convex, with 
numerous concentric striz. Beaks behind the centre pit, very small. Width, 0°2. This was 
found in so very recent a fossil deposit, as to induce Mr. Conrad to suppose that it may still be 
found on the coast, but overlooked on account of its size. Virginia. 
FAMILY MYTILIDA:. 
Anima. oval, moderately thick, with its mantle open throughout its lower portion and 
adhering towards its edges ; a separate opening behind for the excrements, forming very 
rarely a tube. Foot tongue-shaped, channelled, and with a byssus behind. With a very 
few exceptions, marine. Suext usually with an epidermis, equivalve, very inequilateral. 
Hinge without teeth; ligament linear, marginal, partly included: posterior muscular 
impression very small ; the anterior large. 
GENUS MYTILUS. Linnaeus. 
Animal with the lobes of the mantle fringed about the opening of the vent. Mouth moderately 
large, with two pair of soft triangular labial appendages. Foot slender, cylindrical, with 
a silky byssus at its base and posteriorly. Shell longitudinal, subtriangular; apex acute, 
pointed at base, and fixed by a byssus. Beaks terminal, pointed, nearly straight. Hinge 
lateral, usually without teeth; ligament marginal, deeply seated, rectilinear, partly internal. 
Muscular impressions elongated, club-shaped ; the anterior largest : palleal impression entire. 
Oss. The species of this and the following genus are popularly known under the name of 
Mussels. 
