75 



ad basin emarginatis; costis 20 ad 24 sub-elevatis, laevibus vel 

 minute serratis, squamis annulatis, ad latera numerosis ; colore 

 vario. Long. 1. 85.; lat. 0. 70.; alt. 2.; poll. 



Oval, rather triangular, rather depressed, equivalve ; with 

 tbe posterior side more expanded than the anterior ; auricles 

 very unequal, the anterior being generally much produced ; 

 ribs 20 to 24 slightly elevated, round on the tops and either 

 smooth or very finely serrated, with annulated scales, which 

 are generally obsolete towards the centre of the shell. The 

 author having laid together some 50 specimens of this species, 

 all of which differed from each other in some degree, found 

 that although the extreme varieties, such as f. 151 were 

 scarcely recognizable as belonging to the same species, the 

 intermediate gradations were so minute as to render it impos- 

 sible to divide them. Indies, Molluccas; var. f. 151. Red Sep. 



92. P. cbassicostatus. (pi. xv. f. 111. pi. xvii. f. 152.) 



nob. 



T. sub-rotundata, crassa, sub-ajquilaterali, sub-lsevi ; 

 auriculis ineequalibus, costas squamiferas ferentibus : costis 

 24 crassis, elevatis, sub-quadratis, annulatis, lateralibus 

 squamiferis. Interstitiis fere lcevibus, colore pallide purpureo, 

 vel aurantiaco, intus albo. Long. 4. 50.; lat. 1. 50.; alt. 4. 

 30. ; poll. 



The ribs of this species are much more square and elevated 

 than those of P. senatorius, it is also a thicker and larger 

 shell. Locality unknown. 



93. P. icelandicus. (pi. xvii. f. 159, 160, 161.) Chemn. 

 7. to 65. f. 615. 616. Ostr. Cinnabavina. Dillwyn. 



T. ovali, sub-compressa ; sub-ecquivalvi, sub-sequilaterali, 

 tenui, postice paululum expansa ; auriculis inasqualibus, 

 scabroso-sulcatis ; anticis magnis : costis numerosissimis, 

 insequalibus, minute serratis ; colore aurantiaco, concentrice 

 fasciato ; vel albo, vel purpureo concentrice et radiatim fasciato. 

 Long. 3.; lat. 1. 20.; alt. 3. 25.; poll. 



• A well known oval, nearly equilateral, equivalve shell, with 

 unequal auricles and numerous irregular, unequal, serrated, 

 narrow ribs, which are grouped together in twos, threes and 

 fours. Northern Ocean. 



94. P. asperrimus. (pi. xvii. f. 156, 157, 158.) Lam. 

 Anim. s. vert. vi. p. 174. 



P. rotundato sub-ovali, ventricosa, tenui, sequivalvi, 

 insequilaterali, scabroso-sulcata postice sub-expansa : auriculis 

 inajqualibus, scabroso-sulcatis : costis 25, angulatis, ad latera 

 serratis, ad angulum erecto-squamosis : interstitiis nullis 



