47 
M. Sustruncata. Mont. p 93. and Sup. p. 34, t. 
27. f. 1.—in. t.8. p.71.#. 1. f 11.—Pen. 4. t. 55. 
f. \.—Dor. Cat. p. 38. £. 5. f. 10.—D. p. 141.— 
Turt. B.p. 70.—Turt. C. D. p. 82.—F. p. 427.—~ 
Oval-triaugular, inequilateral, convex, not thick, yel- 
lowish horn colour, regularly striated transversely, one 
side truncated, the other produced in a straight line to 
a rather acute point ; beaks not central, tumid and pro- 
minent, without curvature. 0,60...0,80 Common. 
* * Lateral teeth smooth. 
M. Struntorum. Lin. 1126.—D. p. 1388.—Pen. 4. 
p. 193. #. 52: fi .—Mont. p. 94.—Don. t. 106.— 
Turt B. p. 72.—Dor. Cat. ¢t. 8: f. 3. p. 32.—D. p. 
138.—Turt. C. D. p. 81.—F. p. 427.—Da. Cos. p. 
196.¢ 12. f. 3.—#. M. t. 256. f. 3.—Sub-triangular, 
transparent, convex equilateral, slightly striated con- 
centrically, drab-colour with narrow pale rays; the 
striz are rough at the anterior angle, from which to the 
beak the depression has an obtuse mesial prominence, 
the depression at the opposite extremity is less distinct, 
and the mesial more prominent and compressed : beaks 
and inside purplish, 2.,..22. Common. 
M. Cinerea. Mont. Sup: p. 26.—Turt. B. p. 73. 
—I". p. 428.—Sub-triangular, narrower than the last, | 
transparent, convex, sub-equilateral, truncated at the 
