PETRICOLA.— Pla-e III. 



The robust Petricola. Shell glubose-cuneate, bluish 

 without, blackish-brown within ; anterior side 

 much inflated, rounded, short, rayed with sharp 

 numerous ridge s ; posterior side attenuated, narrow, 

 rather angtilar, depressed and contracted in front 

 of the angle, sharply and conspicuously ribbed 

 behind the angle, truncated at the end ; umboes 

 raised, dorsal margin much sloped. 



SowERBY. Proc. Zool. Soc, 1834. 



Hah. P£ 



Species 21. (Mus. Sowerby.) 



Petricola typica. Pet. testd hrevi, inflatd, subglohosd, 

 CMii'af/i, antice rotunda, ventricosd, tenuiter radiatim 

 striata,; postice subattanuatd, versus tenninmn 

 costellis acutis radiatd, ad tenninum denticulaid, 

 tntncatd ; margine dorsali ante umbones excavate, 

 post umbones declivi. 



The ttpical Petricola. Shell short, inflated, sub- 

 globose, cuneate, anteriorly rounded, ventricose, 

 finely radiately striated ; posteriorly somewhat 

 attenuated, towards the end rayed with con- 

 spicuous sharp riblets, denticulated, truncated at 

 the end ; dorsal margin excavated before the vim- 

 boes, sloped behind them. 



Jonas. Moll. Beitr., p. 2, pi. VII. f .". 



Jfab. Isl. St. Thomas. 



Almost as globose in front as Petricola rohusta. The 

 ribs are finer, and increase gradually towards the 

 end. The shell is much less cuneiform than P. 

 Uthopharja. 



Species 22. (Mus. Sowerby.) 



Petricola divaricata. Pet. testa solidd, suhtra- 

 pezoided, omniuo divaricaiim tenuiter striata ; antici: 

 brevissimd, umbonibus terminalibiis ; poslice oblique 

 truncatd ; margine terminali incrassato, foliaceo. 



The divergent Petricola. Shell solid, rather tra- 

 pezoidal, all over divergentlj' finely striated ; 

 anteriorly very short, umboes terminal ; pos- 



teriorly obliquely truncai.ed ; terminal margin 



thickened, foliated. 

 CheMxVItz. Conch., pi. CLXXII. f IGGC-IClw. 

 Karinio divaricata, Gray. 

 Hab. New Holland. 



Species 23. (Mus. Brit.) 

 Petricola ventricosa. Pet. testd oblongd, infla.td ; 



antici; subrotunJd, tenuiter decussatd ; postice 



crenulatd, sublamellatd, subattenuatd , ad lermimm 



truncatd, intitsfusco pictd. 

 The ventricose Petricola. Shell oblong, inflated ; 



anteriorly somewhat ^rounded, finely decussated ; 



posteriorly crenulated,- rather laminated, a little 



attenuated, truncated at the end, pniiitod brown 



within. 

 De.*;hayes Proc. Zool. Soc. 

 Hab. Panama. 



A much more ventricose shell than Petricola den- 

 tinilata, not beaked ii. front, laminated at the end. 



Species 24. (Mus. Sowerby.) 



Petkicol.v lapicida. Pet. testd solidlhsciild, subtra- 

 pezoided, omnino divaricaiim tenuiter striatd ; 

 antici; brevi ; umbonibus subtermincdibus ; postice 

 prodiictd, rotnndatim angulatd, post angulmn 

 costellis acutis, conspicuis, radiatd; ad tenninum 

 truncatd. 



The stone-destroying Petricola. Shell rather solid, 

 rather trapezoidal, all over divergently finely 

 striated ; anteriorly short ; umboes nearly ter- 

 minal ; posteriorly produced, roundly angular, 

 rayed behind the angle with sharp, conspicuous 

 small ribs ; truncated at the end. 



Chemnitz. Couch., pi. CLXXII. f IGOI-lGCj. 



Karinio costata. Gray. 



Hab. Australia. Mauritius. 



Differing from Petricola divaricata in having strong 



sharp ribs at the posterior end. 



