774 



This date-shaped shell is lightly striated between the laminse, 

 which are duplicate excepting at the back, where they are broad, 

 thin, and single. 



Hah. ? Cuming^s collection. 



10. Petricola elliptica (pi. clxvi. f. 10), 8owerhy, Pro. 

 Zool. Soc. 1834, p. 46. 



"V. testa ovato-elliptica, rufescente-albida ; radiatim costatti, 

 postice Isevi; lameUis concentricis sparsis; lunula antica dis- 

 tincta.''^ 



With something of the general form and radiating ridges of 

 Petricola, it has the concentric ridges of the Venerupes j between 

 the ribs it is smooth behind. 



Pound in hard mud at low water ; Payti, Peru. Cuming. 



11. Petricola solida (pi. clxvi. f. 9), Sowerhy, Pro. Zool. 

 Soc. 1834, p. 46. 



V. "testa subgloboso-elliptica, pallescente umbonibus extremi- 

 tatibusque ambabus fusco-violaceis ; radiatim costata, postice laevi- 

 gata ; lineis incrementi nonnunquam sublamellosis postice magis 

 eminentibus." 



Although this shell is more solid, ventricose, and rounded than 

 V. elliptica, 1 more than suspect it is but a variety of that species. 



Pound in hard clay and stones at low water at Lambeyeque, in 

 Peru. Ciimincj. 



12. Petricola lithophaga (pi. clxvi. f. 18, 19), Retzius 

 (Venus), Trans. Turin. P. striata, Lam., An. s. vert. ed. 2. vol. 

 vi. p. 158. Mya decussata, Tnrt. P. costellata. Lam. ib. P. 

 roccellaria. Lam. ib. P. ruperella. Lam. ib. Venerupis petricola, 

 Blainv. Spha^ria decussata, Turf. 



Pet. testa irregulari, inaequilatera, antice brevi, rotundata, pos- 

 tice aperta oblique attenuata, striis radiantibus antice tenuibus pos- 

 tice validioribus. 



The varieties included in the above synonyms differ from each 

 other in the lightness or solidity of the shell, in the strength of 

 the ribs, and in shape ; but they are all short in front, and ob- 

 liquely taper off at the base, where the radiating striae are streng- 

 thened. The following five species appear to differ more essen- 

 tally. 



Britain. 



13. Petricola typica (pi. clxvi. f. 21), Jonas, MoUusc. Beitr. 

 p. 2. pi. 7. f. 3. 



