775 



Pet. testa P. robustce simili, sed tenuiore, striis radiatis gra- 

 datim crescentibus ; omnino alba. 



Almost as globose as P. robusta, but without any colour, and 

 lighter, with the ribs more gradually increasing in size and dis- 

 tance towards the back. 



Island of St. Thomas. 



14. Petricola robusta (pi. clxvi. f. 16, 17), Sowerby, Pro. 

 Zool. Soc. ] 834. f. 4. 



"Pet. testa rotundato-subtrigona, gibbosa, solidiuscula ; extus 

 rufescente-fusca, intus nigricante ; radiatim costata, costis anticis 

 tenuioribus confertioribus, posticis altioribus ; interstitiis omnibus 

 exilissiine decussatim striatis ; latere antico rotundato, postico 

 subacuminato ; margine dorsali deelivi." 



Of a dull orange tint, with purple at the apices and blackish 

 inside, rather thick, very globose in front, tapering behind, where 

 the valves are unequal, the right valve slightly overwrapping. 

 The radiating stria? are distant, numerous, and close in front, but 

 towards the back become separated, strong, acute; the hinder 

 ones of all are a little smaller, serrated, and their ends form a 

 denticulated edge. 



In rocks, six to eleven fathoms, at Panama. Cuming. 



15. Petricola bipartita (pi. clxvi. f. 20), Deslwyes, Pro. 

 Zool. Soc. 1853. 



"Pet. testa, elongata subtrigona, antice turgida, obtusa, brevi, 

 postice attenuata, subangulata, cuneiformi, intus extusque candi- 

 dissima, longitudinaliter striata ; striis in latere antico multo tenuio- 

 ribus divisis, divaricatis, irregulariter inter se conjunctis, in medio 

 regularibus, sensim in latere postico crassioribus ; valvis tenuibus, 

 dentibus cardinalibus inasqualissimis, uno in utraque valva magno 

 robusto ; sinu pallii trigono, basi lato, in medio valvarum posito." 



Much resembling P. UthopTiaga, but with the hinder ribs more 

 distinct and serrated, and the front ribs divided and diverging. 

 It is also less oblique than the British species. 



Island of Samar, Philippines. Cuming. 



16. Petricola Chinensis (pi. clxvi. f. 15), Deshayes, Pro. 

 Zool. Soc. 1853. 



"Pet. testa ovato-subtrigona, antice obtusa, turgidiore, brevi, 

 laevigata, postice attenuata, in medio et postice longitudinaliter 

 sulcata, sulcis undulatis convexis interstitiis latioribus, umbonibus 

 minimis, oppositis, separatis; ligamento magno crasso; cardinali- 



