255 



PI. vii. fig. 13; o^ pentamerus, PL x. fig. 7 ; amplexus, PI. vi. 

 fig. 16, and oi conularia, PI. vi. fig. 17, imparted, in all pro- 

 bability, to their inhabitants, a power of a similar kind. 

 The fissure, noticed in one of the valves of the shells 

 bearing a close analogy with the productus of Martin, and 

 figured, Organic Remains, Vol. iii. PI. xvi. fig. 10, may, 

 with reason, be supposed to have been also part of an ar- 

 rangement for enabling the animal to accomplish a corres- 

 ponding process. 



But the existence in the mountain limestone, and others 

 of the early strata, of shells bearing the form of the snail- 

 shell, is a circumstance so apparently contradictory to the 

 notions which have been just suggested, and, indeed, to opi- 

 nions which are very generally entertained, that it should 

 not pass as supported by the authority of Mr. Sowerby, 

 without determining how far that authority has really been 

 given. 



The first fossil of this kind, which was noticed by Mr. 

 Sowerby, is helix carinatiis, (Min. Conch. Tab. x.) found in 

 the grey limestone, near Settle, in Yorkshire ; after which 

 he saw the cast of a shell found in the micaceous sand form- 

 ation near the Devizes, helix gentii, of which he says, " I 

 presume it to be an helix., as somewhat according with 

 Tab. X." But on the subsequent examination of two other 

 fossils of the mountain limestone, Mr. Sowerby was led to 

 observe, " Had not the general form strongly resembled the 

 helix above-mentioned, I might have been induced to have 

 placed this as a trochus, although it does not positively 

 accord with the characters of that genus. I might have 

 formed a new genus of the two, to which the following 

 species should have been added, did they not differ mate- 

 rially from each other in the characters which should dis- 

 tinguish it ; besides, the aperture is very imperfect in them 

 all. It is probable that other species may be found, and 

 that by their help, and that of more perfect specimens, the 



