34 TESTACEOUS MOLLUSCA. 
M. Saux. Gray. Annals. Nat. His. 1. Oval, sub-triangular, 
very depressed and thin, smooth, polished, sub-equilateral, rounded 
at the sides, pale yellowish with crowded pale chesnut rays ; slopes 
not striated, nor depressed, each with a transverse bar of ‘chesnut ; 
inside uniform white, the lateral teeth laminar and moderately dis- 
tant, the v-shaped tooth large. 14..2. 
M. Nucuevs.. | Conr. Jour. A. N.S.. Phil. 6. ¢. 11. f: 4. 
Small, triangular, thick, with an obsolete concentric ridge ; umbones 
flattened and rectilinear, apices sub-central and very acute; one of 
the slopes depressed ; lateral teeth strong; inside pale brown. 4.— 
New Jersey. 

1 See also the M. Cuneata of Chemnitz, f. 215. (D. 135.—W. t. 
6. f. 10.) figured with the hinge of Mactra and an external carti- 
lage! We have given a copy. See too the M. Achatina, Chemnitz. 
CWE 6. 6.572205) 
To this genus may be attached the Mutinr# of Gray, which are 
thus characterised in the Magazine of Nat. History for 1837. 
“ Ovate, trigonal, sub-angular at each end. Teeth like Mactra. 
Siphonal inflection ovate, distinct. Ligament internal! ina tri- 
angular groove in the upper surface of the deep oblique cartilage 
pit, quite hidden. 
* Anterior slope circumscribed by a raised line. 
M. Tyricus. Gray. Ovate, suborbicular, convex, solid: um- 
bones wide apart: area lozenge-shaped : lateral teeth very short, 
high, thick, round : cartilage pit projecting into the cavity of the 
shell. 
M. Bicotor. Gray in Mag. N. H.1837. Ovate, rather con- 
vex, solid, white ; umbones and anterior slope, orange, varied : 
lateral teeth short, compressed, triangular; cartilage pit projecting 
mto the cavity of the shell: (in the young, the anterior slope sepa- 
rated by a distinct line : umbones brownish.) 
** Trigonal, anterior slope flattened. 
M. Larerauis. Gray.—Macr. L. Say. Jour. A. N.S. Phil. 
2. p. 309.— Gould. f. 34, 5.—Conr. Am. C.t. 14. f. 2. Very 
convex, nearly smooth ; the lateral margins flattened, cordate with 
a straight, sometimes concave profile, the one rounded at the tip, 
the other longer and less obtuse: umbo sub-central, prominent. 
3..43,—N. America. 
M. Donacrrormis. Gray. Mag. N. H. 1837.—Beechey. Z.. 
t. 44. f. 13. Trigonal, anteriorly sub-cuneiform, posteriorly some- 
what rounded; ventricose, white under a thin epidermis : anterior 
slope flattened, keeled on the edge. 2.—S. Seas. 
