258 TESTACEOUS MULLUSCA. 



P. Obliqua. Lam. 2. — Ostrea Alata. Gmel 3399. — D. p. 

 283—Knorr. 6. t. 21. /. 1.— O. Ala-corvi. Ch.f. 581.— O. Per- 

 na. W. 1. 11. /. 78. — P. Ephippium. Sow. G. — Reeve. Sys. t. 

 106. /. 2. Compressed, subovate, obliquely produced anteriorly, 

 very fragile, purplish brown, but pale towards the beaks : hinge 

 margin very short terminated anteriorly by an obtuse angle from 

 which the margin runs in a scarcely incurved oblique line to the 

 obtuse ventral, posterior sinus short and not deep : surface not stri- 

 ated by radiating lines : edges very acute. 2J. Antigua. 



P. Isognomon. Lam 3. — Ostrea O. Lin 1149. — D. p. 282. 

 Elongated, rather solid, dark chocolate brown, compressed, hinge 

 margin forming anteriorly a longer or shorter lobe-like wing ; sur- 

 face often obsoletely subradiated by costellae ; internal nacre bluish 

 white. Far. A. (Ch. f. 584.— W. t. 11. /. 79.— Bl. t. 63. /. 1. 

 — E. t. 176./. 1.— Sow. G.f. 1.— Reeve t. 106. /. 1.) The body 

 and elongated wing, nearly straight and nearly at right angles dor- 

 sally, so that the shell presents a rude resemblance to a carpenters 

 square. Var B. The wing almost obsolete. (P. Femoralis. 

 Lam. 5.—Ch. f. 582, 3.—Knorr 4. t 10./. 1, 2.—E. t. \15. /. 4, 

 5.) Var. C. (Seba 3. t. 91. / 7.) Wing moderate, body obli- 

 quely curving anteriorly. 6. Indian Ocean. 



P. Avicularis. Lam. 4. — Delt.\4>.f. 3. Compressed, whit- 

 ish, terminating ventrally in a broad oblique lobe : dorsal edge 

 forming a short lobe anteriorly ; beaks conical and somewhat pro- 

 duced : sinus for the byssus profound. Allied to the last. 



P. Canina. Lam. 6.— Seba. 3. t. 91. /. S.—Knorr. 6. t. 13. 



/. 1. Compressed, triangular, rather broad dorsally, somewhat 



lobed on one side, violet brown : shell attenuated and elongated 



towards the ventral edge. 4. Indian Ocean and Australia. M. 



DerJiayes considers this to be the young of Isognomon. 



P. Marsupium. Lam. 7. Ch. f. 577 . Compressed, brownish, 

 rounded ovate ; posterior side with a deep sinus at its junction 

 with the hinge which has but from six to eight teeth : nacre, violet 

 within. Var. — Elongated and squarish : silvery within. New 

 Holland. 



P. Sulcata. Lam. 8. — Ostrea Perna. Lin. 1149. Obovate, pale, 

 yellowish, or the colour of rotten wood, with crowded elevated 

 narrow ribs, which are rendered subnodulous by the layers of 

 growth, the interstices lineated with a darker colour, usually ferru- 

 ginous or purplish brown : hinge-margin rather short, anteriorly sub- 

 auriculated, the anterior edge slightly convex in the young, in the 

 adult nearly straight; sinus for the byssus in one valve only, deep, 

 short : ventral edge arcuated, internal nacre silvery white, cardinal 

 sulci few. 2J..2. New Holland. This is not the shell which La- 

 marck's synonyms refer to, bat is described from an examination of 



