108 
Z. M. t. 72. f. 2.—Somewhat triangular, very flat and 
angular anteriorly, regularly striated transversely, 
clothed with foliations which are serrated on one side, 
white and opaque under the cuticle. 2...13. W. Coasts. 
M. Discors. Turt.B.p.201. ¢: 15. f. 4,5.—F .p.413. 
—Mytitus D. Lin. 1159.—Mont. p. 167.—M, Dis- 
CcREPANS. Lam. 15.—Da. Cost. ¢.17. f. 1.—Pen. 4. p. 
167.— Inn. T. 8. p. 111. &. 3. f. 8.—Dor. Cat. p. 40. 
t.2. f.1.—D. p. 319.—Turl. D. p. 112.—Oval, very 
tumid anteriorly rather pointed and somewhat contracted 
at the ventral margin; divided into compartments, the 
central being nearly smooth, the extremes with longitu- 
dinal ribs; cuticle green or brownish horn-color ; beaks 
quite terminal, very obtuse and twisted into a single 
flat volution. 0,44. W. Coasts and Ireland. 
M. Discrepans. Turt. B. p. 202.—F. p. 413.— 
Mytirus D. Mont. p. 119. and Sup. p. 65. t. 26. f. 
4,—Tin. T. 8. p. 111. t. 3. fi 9.—Pen. 4. p. 241.— 
D. p. 319.—Turt. D. p. 112.—Oval, flattish, rounded 
anteriorly, slightly ribbed longitudinally at both ends ; 
beaks not quite terminal. 3. W. Coast and Ireland. 
Like the last but flatter broader and rounder at the 
end opposite the hinge, where the ribs are only eight in 
number, the color too is blacker. 
