122 



O-f) 7. Placunanomia alope. 



Upper valve flat, smooth, radiately striated. Scars two, well sepa- 

 rated, rounded, equal-sized. 



Hah. California ; Lady Katherine Wigram. 

 Two upper valves in British Museum. 



ff European. 



8. Placunanomia patelliformis. 



Shell suborbicular, convex or quite flat, radiately striated ; iimer 

 disk greenish. Apex rather within the dorsal margin. 



The upper muscular scar of the dorsal valve very large, oblong ; 

 the lower one small, roundish, on the lower part of the hinder margin 

 of the upper one. 



The pedmicle of the cartilage with a triangular cavity in front, 

 under the tip, and continued in an oblong rib-like ridge towards the 

 centre of the shell. 



Anomia patelliformis, Linn. S. N. 1152; Nov. Act. TJpsal. 1773, 

 i. 42. t. 5. f. 6, 7 ; Retzius, Nov. Gen. Test. ii. ; Sars, fide Mus. Cu- 

 ming ; Loven, Moll. Scand. 30 ; Forbes ^ Hanley, Brit. Moll. 334. 

 t. 56 ; Wood, Index Test. t. 10. f. 10, not Chemn. 



Squama Magna, Chemn. Conch, vii. 87. t. 77. f. 697. 



Anomia Squama, Gmelin, S. N. ; Schumacher, Essai. 



Ostreum striatum, Ba Costa, Brit. Conch. 162. t. 11. f. 4. 



Anomia undulatim striata, &c., Chemn. Conch, viii. 8. t. 77. f. 699. 



Anomia undulata, Gmelin, Syst. Nat. i. 3346 ; Mont. Test. Brit. 

 157. t. 4. f. 6 ; Maton ^ Racket, Trans. Linn. Soc. viii. 103 ; Turton, 

 Conch. Diet. 4. Bivalves, 230. t. 18. f. 8, 9 ; Dillw. R. S. i. 289 ; 

 Wood, Index Test. t. U. f. 9. 



Ostrea striata, Pulteney in Hist. Dorset, 36 ; Donovan, B. Shells, 

 ii. t. 45 ; Mont. T. B. 153, 580. 



Anomia striata, Loven, Index Moll. Scand. 29 ; Forbes ^ Hanley, 

 Brit. Moll. 336. t. 55. f. 1, 6. t. 53. f. 6. 



Hab. Coast of Europe. British Seas, Lister. North Sea, Sars, fide 

 Mus. Cuming, n. 51. 



This species is easily known from the other European species by 

 being generally thicker and regularly radiately ribbed, and greenish ; 

 but the number and position of the muscular scars at once separate it 

 from all the multiform varieties of that species. Some authors, over- 

 looking the latter character, have been inclined to regard it as a mere 

 variety. 



I may remark, that the large series of this species which I have 

 examined has shown that the position of the two muscles is liable to 

 a slight variation ; in by far the larger number of specimens the small 

 lower muscle is quite close to and confluent vnth the scar of the upper 

 larger muscle, but in a few specimens it is separated from the upper 

 larger one by a small interval or space. This has induced me to be- 

 lieve that probably the three West Indian species of the genus may 

 prove, when a larger series of specimens have been collected and com- 

 pared, only varieties of the same species. 



