TYE : NOTES ON THE EPIDERMIS OF MOLLUSCA. 223 



The colouring of the UtiionidcB is due to the epidermis. 



It varies in texture and pattern in different genera and 

 species, being sometimes studded with barbed blades as in 

 Mytilus barbatus and M. modiolus. In Buccinum, Fusus, Triton, 

 and others it consists of a complete network of short blades. 

 Some species have a roughened or hispid epidermis before birth 

 and retain that appearance for a short time only, losing it as they 

 grow older. Several of our species of Planorbis shew this. 



Pla7ioj-bis albus var. Draparnaldi has from 45 to 50 ridges 

 extending round the whorl, each of which bear close rows of 

 three bristles each on a ridge or wrinkle of the epidermis. 



Planorbis contort us and P. corneus are both beautiful micros- 

 copical objects when newly hatched out. Both our English 

 species of /'cr/z/^Z/Vzi^ are hispid when born, P. cofitecta having the 

 longest hairs. 



Beautiful examples of the hispid periostracon are to be found 

 in the genus Helix, the species bearing it are widely distributed. 

 I am familiar with many from Europe, Asia, America, and 

 Australia. 



It occurs in every stage of development roughened, dotted 

 with points or incipient hairs, to frills of long hairs or bristles, 

 plaited {H. lamellata) or in a lovely coronet of spines {H. acideata). 



It is noticeable that all our hispid Helices spend their life in 

 damp places, hence none of them are brilliantly painted, but like 

 the human sojourner in mental or material darkness shew few of 

 the attractive attrilmtes of Hght. Beautifully coloured Helicidae 

 are destitute of hairs. It is worthy of note that so far as I have 

 observed the more globose (hispid) species of this family have 

 the shortest and stoutest hairs, the flatter-spired ones the longest. 



These hairs possess the property of becoming erect when 

 brought into contact with moisture, no matter how pressed 

 down they are — and they are apt to become so during seasons of 

 rest — so soon as they are damped they immediately form a per- 

 fect cheveaiix-de-frise. 



