GASTEROPODA. 45 



much produced in the English specimens ; and that author speaks of his shell as 

 pointed at the apex : Sa s^pire allongee et pointue au sommet se compose de sept 

 tours trcs convexes, ordinairement lisses dans les individus f ossiles del'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 maybe 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 stria? 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 strias ; 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 pro- 

 bability of the Purpura incrassata being a variety of the P. lapillus. 



M. Philippi (En. Moll. Sic. p, 179) enumerates this species among the Sicilian 

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

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

 by him Fitsns sinistrorsus. On a comparison I have made with 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 

 considered 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 occasionally 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 dextni 1 

 variety, such as are sometimes found among other species, and are probably pro- 

 duced by an inversion of some of the important viscera. 



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

 ing to Mr. Bean ; it was found in the Mammaliferous Crag of Bridlington. 



