59 
Puorapis. Lam.—Turt. B. p. 20. t. 2. f. 10.— 
Mytizus 8: Lin. 1156.—Pen. 4. p. 110. t. 63. f. 72 
—D. p.304.—Mont. p. 164.—Dor. Cat. p. 39. t. 13 
f. 5.—Turt. D. p. \13.—Lin. T. 8. p. 270. t. 6. f.3, 
4,.—List. t. 426. f. 267.—Rounded posteriorly, sub- 
truncated anteriorly, the ventrel edge slightly incurved 
near the middle, dull white under a greyish wrinkled 
cuticle, coarsely wrinkledtransversely, 4.,.14. Common, 
in Rocks. 
H. Arctica. Lam.—F. p. 461.—H. Minuta. and 
Oxstona. Turt. B. p. 24. t. 2. f. 12, 3.—Soren M1- 
nutus. Lin. 1115.—Mont. p. 53. t. 1. f. 4—Ch. f. 
51, 2.—Wood. G. C. p. 139. ¢. 34. f.5, 6.—D. p. 
69.—Turt. C. D. p. 161.—With two diverging spinous 
ridges on the anterior slope; closely resembling the 
former specicsin age by the gradual disappearance of 
the spinous ridges, but distinguished by the greater 
incurvation of the ligamental edge. The Mytilus 
Precisus of Mont. p. 165. t. 4. f. 2. seems but a 
variety of this species. 
GrEnus.—AGINA. Turton. 
Transverse, oval, equivalve, inequilateral, open at the 
anterior end; hinge with a single erect conic per- 
