PETRICOLA.— Plate I. 



Species 4. (Mus. Brit.) 



Petricola dacttlus. Pet. tcstd oblonga, vald'e inflatd, 

 plioladiformi ; antice jiaulb hianti, acmniimtd, 

 costis decumlentibus, sen-atis, suhdupUcatis usque 

 ad medium radaM ; ad medium ventricosissimd ; 

 postice attemiatd, radiatim striatd, ad terminum 

 truncatd, margine doisali deelivi, ventrali acclivi. 



The date Petricola. Shell oblong, much inflated, 

 pholas-shaped ; anteriorly a little gaping, acu- 

 minated, rayed as far as the middle with decum- 

 bent, serrated ribs very ventricose at the middle ; 

 posteriorly attenuated, radiately striated, truncated 

 at the end, dorsal margin sloped downwards, ven- 

 tral sloped upwards. 



SowERBT. Genera of Shells, fig. 3. 



Hah. South America. 



Species 5. (JIus. Brit.) 



Petricola elegans. Pet. testa oMongd, antice paulo 

 hianti, acuminata, concentrice laminatd, radiatim 

 striatd, ad" medium infiald, postice ante angulum 

 depressd, post angulum, laminis latioribus, ex- 

 tantibus, exfoliatd, ad termimim tnmcatd ; margine 

 dorsali ante iimbones excavato, post vmbones suh- 

 declivi. 



The elegant Petricola. Shell oblong, anteriorly a 

 little gaping, acuminated, concentrically laminated, 

 radiately striated, inflated in the middle, pos- 

 teriorly depressed in front of the angle, exfoliated 

 behind the angle with broader lamina;, truncated 

 at the end ; dorsal margin excavated before the 

 umboes, somewhat sloped behind them. 



Desha YES (Venerupis). Proc. Zool. Soc, 1853. 



Hab. ? 



Named by M. Deshayes from a shell in the Cumingian 

 collection. 



Species 6. (Mus. Brit.) 



Petricola cultellus. Pet. tcstd plwladifoi-mi, ohlongd, 

 antice rotundd, brevissimd, costis serratis acutis, 

 siihdistantibus radiatd ; postice elongatd, attenuatd, 

 striis elevatis, crebris oblique radiatd, ad tcrminwn 

 acuminatd. 



The pruning-knife Petricola. Shell pholas-like, 

 oblong, rounded anteriorly, very short, rayed with 

 serrated, sharp, rather distant ribs; posteriorly 

 elongated, attenuated, obliquely rayed with 

 elevated, close striae ; acuminated at the end. 



Deshayes. Proc. Zool. Soc, 1853. 



Hab. Ceylon. 



In Petricola phola.diformis the front ribs are strong, 

 rather biangular and distant. In the present species 

 they are sharp, have a single angle, and are less 

 distant. 



Species 7. (Mus. Sowerby.) 



Petricola pholadiformis. Pet. testd oblonga, sub- 

 cylindricd, antice rotundd, brevissimd, costis validis, 

 distcmtibus, suhquadratis radiatd, postice elmigatd, 

 attenuatd costellis acutis, elevatis, crebris, oblique 

 radiatd, ad terminum acuminata. 



The PnoLAS-LiKE Petricola. Shell oblong, sub- 

 cylindrical, anteriorly rounded, very short, rayed 

 ■with strong, distant, rather square ribs, elongated 

 posteriorly, obliquely rayed with sharj), elevated, 

 close riblets, attenuated at the end. 



Lamarck. Anim. s. Vert., Petricola, No. 11. 



Hab. North America. 



The external appearance of this well-known species 

 is that of a Pholas ; and it is only the absence of the 

 subunibonal processes and accessory valves that dis- 

 tinguishes it, as far as the shell goes, from that family. 



