JEFFERY : ON THE HAIRS OF MOLLtJSCA, &C. 2 1 



With regard to the inclination of the bristles, so far as I 

 have been able to ascertain, they appear in H. hispida to be 

 directed forward towards the naouth of the shell on the left 

 periphery, and of course, following the whorl round, they point 

 backwards on the right side. 



In H. sericea they are nearly perpendicular, with no regular 

 inclination, except that on the recurved and thickened portion 

 of the mouth of the shell, the curvature of the shell here 

 causes them to point backwards. 



In H. obvoluta the tendency seems to be rather the reverse 

 to that in H. hispida, but I cannot speak positively without 

 more time and further observation. 



The only species in which the bristles are decidedly per- 

 sistent, and we may say permanent, is H. sericea. 



I have not seen a specimen in which any great amount of 

 denudation has taken place and the bristles are not easily 

 detached in any quantity with a penknife. 



Of the uses of these bristles, I will not attempt to offer an 

 opinion, it is a subject which cannot be treated on by one 

 whose study of the moUusca has been confined to our own land 

 and freshwater forms, at all events in so short a space of time 

 as I have had at my disposal during the past year. 



A botanical friend of mine tells me that what I have called 

 spines on the Holly and Thistle are considered by botanists as 

 hairs only, and that spines are such only as contain a portion 

 of woody substance, as in the case of the Whitethorn, Black- 

 thorn, &c. 



Therefore with the impression that these epidermal hairs, 

 formed with the first or outside layer of shell, are composed of 

 the same matter only as the epidermis, and would, from a 

 botanist's point of view, be designated simply as hairs and not 

 spines, I have contented myself by writing of them as hairs or 

 bristles. 



