SYKES : VARIATION IN RECENT MOLLUSCA. 257 



Tellina incarnata has been observed with only one siphon and no 

 labial palps. 



Bloomer' found that in Anodonta the animal is able to repair even 

 extensive damage to the mantle-lobes, but is not able to make good 

 injuries to the gills, and that the mollusc can live and thrive with 

 aborted respiratory organs. 



Amongst Cephalopods, we may refer to a specimen of Eledone 

 cirrosa, examined by Appellcif,^ in which not only was the third left 

 arm developed as hectocotylus as usual, but also the third right arm. 



The operculum, we are all aware, may be present or absent in 

 members of the same group, but it does not seem to be so generally 

 known that it may be present or absent in the same species. Of 

 a series of Volutharpa ampiillacea examined by Dr. Dall, the majority 

 were without opercula or any trace of the pad-like area from which 

 the operculum is secreted, some had traces of this region, and others 

 well-developed opercula. The bioperculate Biiccinum undatum are 

 well known, and a specimen has recently been taken off Unst.^ Clark 

 found that every specimen of Trochus lineatus from one spot near 

 Exmouth had distorted opercula, a fact which Jeffreys referred to 

 some disease of the opercular lobe. 



The epiphragm formed by many shells when sestivating deserves 

 more consideration than it has received. It would be interesting to 

 know how far the same form is constant in a genus, and what the 

 explanation of those curious structures noticed in the specimens of 

 Thaumastus, figured recently* in our Proceedings by Mr. Smith, 

 may be. 



There seems to be but little relationship between the colour of the 

 animal and that of the shell. Many colours are seen in the animals, 

 Camerano * stating that black is rare ; brown, grey, yellow, white, and 

 red, common ; violet, fairly common ; blue, not rare ; while green is 

 infrequent. His observations also led him to the belief that animals 

 with sti'ong shells were more highly coloured than those with fragile 

 shells. All parasitic molluscs appear to be white. Age seems to have 

 some effect, as also food, while conditions of temperature have been 

 observed to be correlated with slug-coloration. In Germany it has 

 been noticed that warmth either inhibits black or causes it to disappear, 

 while exercising an opposite effect on red. Limax arhorum has been 

 noticed to be spotted with black on the plains and of normal 

 coloration on the hills.^ In this connection a very interesting paper 

 by Simroth ' should be studied. Collinge,* studying the colour of the 

 foot-fringe of Arion empiricorum, found extraordinary variation, which 



' Journ. Malac, vol. vii, p. 138. 



* Bergens Mus. Aaibng, 1893, p. 14. 



■' Standen : Journ. Conch., vol. xi, p. 62. 



* Ante, p. 3. 



* Mem. Ace. Torino, vol. xxxvi, pp. 348-349. 

 ^ Cockerell : Zoologist, ser. in, vol. x, p. 341. 

 '' Nachrbl. Malak. Ges., xviii, pp. 65-80. 



* Joiuu. Malac, x, p. 19. 



