49 



that of the under valve being generally of a reddish brown, 

 softened into purjile or white towards the umbones and 

 auricles ; in the upper valve being variegated with white 

 spots, interrupted rays of ])rown and zigzag lines; in one 

 variety the upper valve is nearly l)lack, and the under valve 

 white, with fulvous lines in the grooves. Mr. Cuming has 

 specimens from the Red Sea and the Philippine Islands. 



11. P. DENTATUS. (pi. XV. f. 105, 106.) Sow. Zool. Proc. 

 1835. p. 109. 



'' T. valde ineequivalvi, eequilaterali ; auriculis eequalibus, 

 valva (sinistra) planulata, sulcato-radiata et striata, altera 

 valde convexa, laevigata, radiatim sulcata, margine ventrali 

 profande dentato : long. 3. 75.; lat. 1. 5.; alt. 3. 5. poll." 



The edges of the ribs are deeply cut in the form of teeth, 

 and the edge of the upper valve falls deeply within. St. Elena. 



12. P. Erythrceensis. (pi. xviii. f. 163, 164.) ? 



T. rotundata, ventricosa, Isevi ; auriculis concavis, magnis ; 



valva sinistra concava, costis concavis, medianis, distantibus 

 novem ; ad latera utrinque tribus minoribus ; valva dextra 

 costis duodecim, rotundatis, latis, ad marginem valvam alteram 

 superante ; colore albo-lutescente, rubro-variegato, umbonibus 

 purpureo-tinctis, interne fusco-purpurascente. Long. 2. 10; 

 lat. 0. 60. ; alt. 2. ; poll. 



The general character of this species is similar to that of 

 P. fuscus, but the shell is narrower, and the ribs fewer in 

 number and flatter, those in the upper valve being crossed 

 with lines and spots of red. Found in coral sand in the Red 

 Sea. 



13. P. PYXiDATUs. (pi. xii. f. 24, 25.) Born. Mus. Cses. 

 Vind. t. 6. f. 5, 6. Ostrsea sulcata, Gmel. 



T. insequivalvi, rotundata ; auriculis sub-sequalibus, magnis, 

 costatis ; valva sinistra complanata, prope umbones excavata, 

 costis viginti-duobus, angustis ; distantibus et minoribus, 

 numerosis, lateralibus, interstitiis latis, complanatis, valva 

 dextra ventricosissiraa ; margine alteram superante, costis 

 leevibus, latis, interstitiis nullis. Long. 2. 40 ; lat. 0. 60. ; alt. 

 2. 20. ; poll. 



Inequivalve, orl)icular ; the auricles large and nearly equal, 

 with several fine costee ; the upper valve flat, inversely 

 hollowed near the umbones, the ribs, twenty-two in numl^er, 

 are narrow and distant, with some smaller ones at the sides, 

 which are rather elevated, the interstices are mde and flat ; 

 the dextral valve is very ventricose, the margin over-reaching 

 the other, the ribs are smooth and Avide, with no interstices. 



F 



