47 



prope umbonem sub-concava, lateribus paululum elevatis ; 

 auriculis eequalibus, latis, concavis, prope marginem sulcatis ; 

 costis in valva sinistra 14, angustatis, ad latera angulatis, 

 planis, in valva dextra 16, latis, divisis, depressis, sub-rotun- 

 datis ; interstitiis in valva sinistra latis, planis, in medio sub- 

 eostatis, in valva dextra angustatis ; colore albo-lute scente vel 

 fusco, rubro-maculato vel rubro, albo-maculato vel purpureo 

 fasciato. Long. 3. 30. lat. 0. 80. ; alt. 2. 80. ; poll. 



The ribs in the upper valve are narrow, and angulated at 

 the side, those of the lower are broad, and generally divided 

 in the centre, the breadth of the ribs in the lower valve corres- 

 ponding with the broad interstices in the upper. 



West Indies. 

 6. P. sulcicostatus. (pi. xiii. f. 35, 36.) nob. 



T. rotundata, radiatim sulcata, sub-ventricosa ; auriculis 

 latis, excavatis, striatis ; costis 12, in valva sinistra elevatis, 

 sub-quadratis, sulcatis ; in valva dextra rotundatis, striatis, 

 interstitiis in valva sinistra mediocris, sulcatis, in valva dextra 

 sub-nullis; colore valvee sinistree pallide fulvo, rubro-fulgurato, 

 valvje dextree purpureo. Long. 1. 65.; lat.O. 50.; alt. 1. 50; 

 poll. 



Rounded, radiately sulcated, rather ventricose ; the auricles 

 wide, concave, striated; the ribs 12 in number, in the left 

 valve elevated, rather square, sulcated, in the right valve 

 rounded and striated, with scarcely any interstices. The 

 interstices in the left valve are as wide as the ribs, and 

 sulcated. The colour of the left valve is pale fawn, with 

 angulated streaks of red, in the right valve it is purple. From 

 Mr. Norris's Collection. 



7- P. sub-viridis. (pi. xviii. f. 165, 166.) nobis. 



T. sub-rotunda, sub-ventricosa; valva sinistra prope um- 

 bonem concava, lateribus elevatis; auriculis latis, rectangulatis, 

 concavis, prope marginem sulcatis ; costis centralibus 13, in 

 valva sinistra elevatis, rotundatis, kevibus; lateralibus minori- 

 bus : in valva dextra, obsolete sulcatis, rotundatis, interstitiis 

 concentrice striatis, colore valvee superioris fusco-viridescente, 

 valvee inferioris albo, ad umbonem luteo, in medio sub-fusco. 

 Long. 2. 20. ; lat. 0. 60. ; alt. 2 ; poll. 



Resembling P. Jacobceus in form, but less spread at the 

 sides,with the deep valve more ventricose, and the ribs in both 

 valves rounded and nearly smooth ; the upper valve is of a 

 greenisli brown colour. 



8. P. fuscus. (pi. xvi. f. 118, 119.) Klein. 



T. rotundata, ventricosa, leevi ; valva sinistra ad umbonem 



