FOSSIL SHELLS OF THE CRAG. 461 



portance to the geologist, the permanent establishment of 

 species being all that is required for the purpose of identifi- 

 cation ; but upon this point it is certainly to be regretted that 

 there should be any dispute, and until we are well acquainted 

 with a shell in all its varieties and monstrosities, this must 

 and always will be the case. The following are all the Bul- 

 lae belonging to the crag that I have seen ; the descriptions 

 will always be given from my own specimens, unless when 

 otherwise expressed. 



Bulla quadrata, Nob. Suppl. PI. No. vii. fig. 1. 



Shell quadrangular, finely striated, aperture wide, outer lip nearly straight, 

 inner lip folded back, muscular impression marginal. Apex depressed > 

 visible. Length j, diameter T f of an inch. 



Coralline crag, Sutton. 



Only one perfect specimen of this pretty shell has fallen 

 into my hands, therefore I presume it rare ; a few imperfect 

 ones have assisted me in drawing up its character. The 

 quadrate form of the outer lip renders this shell very distinct, 

 and not liable to be confounded with any other species. A 

 slight compression round the upper part of the body-whorl 

 takes a little from the straight line of the outer lip, which is 

 much expanded ; the inner lip is not only folded back, form- 

 ing a small umbilicus, but leaves an elevated ridge inwards, 

 which produces a flattened depression on that side. Muscu- 

 lar impression large and conspicuous ; stria fine, numerous, 

 and diverging. 



I have included this very expanded shell among the Bulla 

 for the reasons above stated, conceiving the expansion of the 

 aperture alone, to be insufficient for generic distinction. 



Bulla catenata, Nob. Fig. 2. 



Shell obovate, spire depressed, visible, aperture large, lip arcuated, vertex 

 truncated, inner lip projecting: sub-umbilicated, striated, sfrk numer- 

 ous, ornamented ; muscular impression indistinct. Length £, diameter 

 ^ of an inch. 



Coralline crag, Sutton. 



Two or three specimens only are in my possession, one of 

 which is sufficiently perfect to exhibit all the characters above 

 described. The elegant chain- like markings that ornament 

 this shell are similar to those of Bulla catena, but in other 

 respects it differs from the description of that species. The 

 inner lip stands prominently forward, causing a depression be- 

 hind it ; the outer one is sharp and arcuated, which gives an 

 oval contour to the shell. The upper part of the outer lip is 



Vol. III.— No. 33. n. s. 3d 



