CO 



T. rotundata, sub-irregulari, iiircquivalvi, sub-ventricosa, 

 sub-kcvi; auriculis sub-sequalibus, striatis; valva sinistra altera 

 magis ventricosa, margine alteram valvara superante ; costis 

 novem, rotundatis, sub-distantibus, sub-depressis ; valva 

 dextra sub-complanata, costis minus clevatis ; colore auran- 

 tiaco immaculato, a t c1 pallide roseo, fulvo concentrice fasciato. 

 Long. 1, 70 ; lat. 0, 50 ; alt. 1, 50 ; poll. 



Rounded, rather irregular, inequivalve, rather ventricose, 

 nearly smooth ; the auricles nearly equal, striated ; the upper 

 valve more ventricose than the lower, overlapping it at the 

 margin ; ribs nine, rounded, rather distant and depressed ; 

 right valve tlattish, with less elevated ribs, the colour is plain 

 orange, or a pale red, concentrically banded with light brown. 



Black Sea. 



45. P. PLEXUOSUS. (pi. xix. f. 200 to 205.) Poll. P. 

 Isabella, Lam. P. polymorphus, Jay. 



T. sub-equilaterali, flabellatim rotundata, j)lus minusve 

 ventricosa, laevi vel obsolete radiatim striata; marginibus 

 plerumque inflexis ; auriculis sub-equalibus, radiatis, rectis, 

 acutangulatis, ad basin emarginatis : costis quinque, magnis, 

 gr'adatim elevatis ; et interdum quinque parvis intermediis : 

 costis internis duplicates, ad margin em dentals : colore vario. 

 Long. 0. 80.; lat. 0. 40.; alt. 0. 75.; poll. 



Some varieties of this species are rather difficult to dis- 

 tinguish from P. glaber, having smaller ribs between each of 

 the rive large elevated ones; the margins are generally inflected: 

 the ribs on the under valve are broader, with a groove in the 

 centre. Mediterranean. 



46. P. vxd flat us. (pi. xix. f. 206, 207.) nob. 



T. P. flexuoso shniliima, sed lateribus magis expansis, margi- 

 nibus angulatim inflexis, costis magis elevatis ; colore, valvfe 

 sinistrae rubro fulvescente, intus purpureo ; valvse dextra) albo, 

 rubro tincto. Long. 1. 30.; lat. 0. 46.; alt. 1. 8. ; poll. 



The difference between this species and the last will be 

 more easily recognizable from the figure than from the descrip- 

 tion. It may be observed however that in P. undulatus the 

 ribs are more widely divergent, much deeper, and slightly 

 knobbed. The whole shell is radiately grooved, the colour of 

 the upper valve is yellowish red outside and purple inside, that 

 of the under valve is nearly white tinted with rose. 



Mediterranean ? 



47. P. clavatus. (pi. xii. f. 14, 15.) Poll. Test. 1, 2. f. 

 17, Including P. inflexus, Poli. f. 4, 5 ? P. aspersus, Lam? 



T. rotundato sub-trigona, ineequivalvi, sub-tequilaterali de- 



