GASTEROPODA. 45 



and that author speaks of his shell as pointed at the apex : " Sa spire allongee et pointue au 

 sommet se compose de sept tours tres convexes, ordinairement lisses dans les individus 

 fossiles de I'Angleterre." None of my specimens have that character, and, in fact, I have 

 not any specimen that is quite smooth, although many are much rubbed and eroded; 

 traces of striae may be detected in all that are in my cabinet. Although specimens of 

 the dextral variety, precisely similar in sculpture to that of the recent shell, are not 

 uncommon in the Red Crag, and it may be worthy of remark, that the general character 

 of this variety is a bicarinated or tricarinated form, while the sinistral one is very 

 rarely so, but resembles the finer strise of the recent shell. This, as it is well known, is 

 one of the most abundant shells in the Red Crag, and at least one of its varieties may 

 be found wherever a section of that formation is visible ; a good series may therefore be 

 supposed in the hands of every collector. Prof. E. Forbes, in his ' Report upon the 

 Geological Relations of the Existing Fauna and Flora of the British Isles,' has separated 

 these varieties, and considers the carinated one as a distinct species. I am not well 

 acquainted with the recent shell in all its variations, but I believe the Crag varieties, 

 above described, to belong to one species. My cabinet contains every possible form 

 of striation, graduating from the carinated ones unto those possessing the finest strige ; 

 but I have not yet seen a Crag specimen with undulations. The extension of variation 

 here given to this species is not more, or even so much, as is allowed by several 

 eminent conchologists, who admit the probability of the Pm-pura incrassata being a 

 variety of the P. lapillus. 



M. Philippi (En. Moll. Sic. p. 1 79) enumerates this species among the Sicilian 

 fossils, which is in all probability identical with the shell now found livino- in the 

 Mediterranean. This is considered a distinct species by M. Deshayes, and named by 

 him Pusus siiiistrorsus. On a comparison I have made wuth some recent specimens 

 in the British Museum, and also with a fossil specimen from Palermo, in the Museum 

 of the Geological Society, I could not detect any character by which it might be con- 

 sidered specifically distinct. The sculpture is different from the recent British 

 specimens ; but, as far as the shell alone can determine the species, it does not differ 

 from some of the Crag specimens, and they can be connected with the other varieties. 



Prof. E. Forbes, in his Report above alluded to, speaks of the dextral variety of this 

 species as its normal condition ; I am rather inclined to think otherwise, and that the 

 sinistral variety was the original form of volution, and not a monstrosity ; and that it 

 has died out in the northern seas, and been replaced by the dextral form, while the 

 sinistral one has retired to the southward. The left-handed specimens, now occasion- 

 ally found in the British seas, may possibly be a remnant of this race : but I am more 

 inclined to believe that they are merely monstrosities of the dextral variety, such as 

 are sometimes found among other species, and are probably produced by an inversion 

 of some of the important viscera 



The carinated variety (f. 1 /) of T. contrarius is figured from a specimen belongino- 

 to Mr. Bean ; it was found in the Mammaliferous Cras: of Bridhnston. 



