Tiiir.R OSTBACEA. 315 



frequently brown, the umbo usually smooth and within bluish green, 

 apex rather within the dorsal margin ; subcentral scars 2, the upper 

 one oblong, very large ; the lower one small, roundish, on the lower 

 part of the hinder margin of the upper one : a dull triangular hollow 

 above the great perforation. 1 ^. Britain, dc. 



A. Striata.* Loven, Ind, Scan. — Brit. Mol. 2, p. 336, t. 55,/. 1, 6, 

 and t. 53,/. 6. — ? Squama Magna, Ch. 697 (from which A. S., Gm. 

 D.p. 290, and W. t, 11,/ 11), copied E. t 171,/ 22, 3. More or 

 less orbicular, resembling the last, but with most crowded rows of 

 regular minute radiating, yet not prickly, scales, in place of ribs : 

 often rayed with ferruginous-brown. 1 L, North Britain, dc. 



A. Cumingii. — Placuanomia C. Brod. Z. P. 1832. — Sow. G. — 

 Penny Cyc. 17, p. 364.— Reeve, t. \23.—Gray, Z. P. 1849, p. 120; 

 Cat. An. p. 9. Depressed, roundish, dull silvery white, margin with 

 3 or 4 very large angular folds ; porforation of lower valve small, 

 lirmly embracing the plug. 2£. Costa Rica. 



A. Rudis.— Placuanomia R. Brod. Z. P. 1834. — Gray, Z. P. 

 1849; Cat. An. p. 10. — Pododesmus Decipiens, Phil. Wieg. 1837, 

 teste Gray. Dirty white, thick, with irregular concentric wrinkles ; 

 inside polished ; subcentral scars 2, rounded, separate, of nearly equal 

 size, the hinder one rather more transverse : perforation moderate, 

 firmly embracing and enclosing the plug. If. Cuba. 



A. Macroschisma. Desh. Rev. Z. 1839; Mag. Z. ISil.—Midd. 

 Mol. Ros.pt. 3,^. 6 ; Sibir. Z. 242, t. 19,/ 1 to 5.— Phil. N. C. 3, 

 p. 132, An. t. 1, /. 4. — Placuanomia M. Gray, Cat. An. p. 11. — 

 Woodw. t. 16,/. 4. Large, irregularly ovate, or suborbicular, inequi- 

 valve, usually thick, greenish white, radiatingly (at times irregularl} r ) 

 ribbed ; inner disk of the upper valve with a large dark green spot : 

 subcentral scars 2, partly confluent on the lower hinder edge, the 

 upper one the larger: lower valve often with a dark green margin, 

 its perforation large, entire, a dull triangular excavation above it. 2. 

 Kamtskatka. 



A. Foliata. — Placuanomia F. Brod. Z. P. 1834. — Gray, Z. P. 

 1849, jp. 120; Cat. An. p. 10. Subdiaphanous, subcircular, rough, 

 subfoliaceous, dirty white, occasionally with very slight distant 

 radiating ribs ; inside of the upper valve splendent, purple-browu 

 in the middle ; subcentral scars 2, nearly united, the upper the 

 larger and rather elongated, the lower small and rounded. W. Indies. 



1 The A. Imbricata of Bruguiere (A. Muricata, D. p. 289, from 

 Ch. 8, vig. at p. 65,/ C. D., copied E. t. 171,/ 14, 5, and W. t, 11, 

 /. 8) seems closely allied, if distinct. 



