76 collinge: a review of the arionid;e of the British isles. 



The cause of this abnormality is a matter of mere speculation. 

 That the animal exhibited some unusual feature is fairly certain, and 

 it seems to me probable that the slit in the mantle, which falls in a 

 line with the perforations, was entirely absent, or, at all events, 

 united at the end near the outer margin of the shell. In this case, 

 as there would be no interruption in the margin of the mantle, a slit 

 or notch (afterwards to be perfected into a complete opening) would 

 not be formed in the shell. 



Jeffreys states that " the number of open orifices in the shell 

 corresponds with that of the tubular folds of the mantle." In the 

 first place, the so-called " tubular folds " are not folds, but merely 

 tentacular filaments, and, in the paper already referred to, I have 

 shown that in reality there are only three of these filaments or 

 tentacles, and that they are always located in the same relative 

 positions upon the edges of the mantle-slit. It was also pointed out 

 that the number of open perforations indicated the length of the 

 mantle-slit, but not the number of the filaments. 



. In addition to this interesting specimen, Dr. Claremont has also 

 presented to the Museum three other very remarkable abnormal 

 examples of the same species. In one there is an enormous 

 development of the columellar surface, giving that part of the shell 

 a solid, heavy appearance. The two other specimens are remarkable 

 for their abnormality of form. This appears to have arisen through 

 injuries received at an early stage of growth, the result being that 

 they became contracted, much raised and arched over the back, with 

 the perforation nearer the margin than usual. 



A REVIEW OF THE ARIONID/E OF THE 

 BRITISH ISLES. 



By WALTER E. COLLINGE, 



Demonstrator of Biology, Mason College, Birmingham. 

 {Continued from p. 66.) 



Arion celticus, Pollonera, 1887. 



"A. hortensis ajfinis : dorsum mediocriter rugosum ; clypeus minute 

 granulosus ; olivaceo - nigricans, utrinque nigro-zonatum, 

 niinutissimc aureo-punclatum, lateribus pallide-griseis nigro- 

 variegatis ; solea pailide-flava ; pedis margo pallide flavus 

 iniperfecte griseo-tineolatus ; caput et tentacuia nigricantia. 

 Mucus soleae et pedis aurantiacus. Long. max. 30 mill." 



