772 



Pet. testa P.pholadiformi simili, sed costellis anticis vix elevatis, 

 interruptis, acute serratis. 



The front ribs are here reduced into radiating rows of sharp 

 points ; still I doubt greatly whether this may not be a mere 

 varietal distinction. 



New Zealand. Mr. Cuming's collection. 



3. Petricola gracilis (pi. clxvi. f. 12), Beshayes, Pro. Zool. 

 Soc. 1853. 



Pet. testa P.pholadiformi simili sed longe graciliore, costellis 

 anticis vix elevatis, acute serratis, postice attenuata, striis subob- 

 soletis. 



Sculptured like P. serrata, but more finely; a much lighter 

 and elongated shell than either it or P. pholadiformis, still very 

 doubtful. 



Had. ? Cuming's collection. 



4. Petricola cultellus (pi. clxvi. f. 2, 5), Beshayes, Pro. 

 Zool. Soc. 1853. 



Pet. testa elongato-angusta, transversa pholadiformi lateraliter 

 compressiuscula inferno convexo-arcuato ; antice brevi posticeque 

 obtusa, hiante albo squalide rufescente longitudinaliter squamulis 

 fornicatis exasperatis ; striis in medio posticeque tenuibus, undu- 

 losis striis incrementi irregularibus interruptis ; umbonibus tumi- 

 dulis approximatis lsevigatis, valvis intus candidissiinis ; sinu 

 pallii elongato, angusto, apice obtuso. 



The form is similar to that of P. pholadiformis ; it has rather 

 sharp serrated ridges in front ; it is rather depressed, of a very 

 pale fawn-colour, and has the ventral margin rather rounded. 



Ceylon. Mr. Cuming's collection. 



5. Petricola dactylus (pi. clxvi. f. 4), Sowerby, Gen. of 

 Shells, f. 3. 



Pet. testa inflata, ovali pallide grisea, intus alba, antice brevi, 

 subacuminata planulatim costellata, medio tumida, costellis latio- 

 ribus, inde subcontracta, costellis numerosis, cancellatis, postice 

 attenuata subtruncata concentrice striata, striis radiantibus obso- 

 letis. 



A very tumid pholadiform shell, differing from P. nivea in 

 being much stronger, and having th<s short front side almost ros- 

 trated, the middle tumid, and the back contracted. The sculp- 

 ture is in flattened ridges to about the middle, then sharper and 

 more numerous, then lost at the back. 



South America. 



