MARSHALL: ADDITIONS TO "BRITISH CONCHOLOGY." 123 



reversed and several carinated examples occurred with them. I can 

 only account for this colony of malformations by the presence of 

 an animal or plant, most likely the latter, being inimical to the Lit- 

 torina. But whatever the cause, it was also in operation during the 

 remote period of the Crag seas, as similar forms occur in the Red 

 Crag formation, and have been figured by Searles Wood. 1 An 

 analogous case occurs in L. littorea monst. turrita, one colony of 

 which lives in Loch Carron, and another in a limited area in Belfast 

 Lough. 



A peculiar specimen from Jersey resembles L. littorea, while one of 

 the latter from Torbay could easily pass for L. rudis. L. zonaria of 

 Bean is the banded form of the type. 



Sowerby's figures (12 and 18) of the type are perfect. Jeffreys' 

 type figure is too coarse and massive, and belongs to the var. globosa. 

 Sowerby's figures of var. tenebrosa are also very good, but Jeffreys' is 

 an exaggeration of it. And Sowerby's fig. 13 is the var. sulcata. 



L. littorea L. — Very rare in the Channel and Stilly Islands. I 

 know of only three instances of its occurrence at Guernsey and two 

 at Jersey in many years, and the Rev. R. W. J. Smart records two 

 from Stilly. Dead shells are of frequent occurrence on the shores of 

 Jersey, but they are importations for edible purposes from Plymouth 

 and the French coast. 



Monst. sinistrorsum. — I believe there have been only four known 

 examples of this monstrosity in Britain, which is remarkable consider- 

 ing the abundance of the species and the enormous quantities collected 

 for the market. The last one, found by a fish salesman, " parted " 

 for 30/-, but as much as ^5 has been paid for one. 



Another monstrosity occasionally met with has a double aperture. 

 This very curious " sport " probably arises from the Littorina becoming 

 wedged in a crevice of rock with its mouth more or less blocked, 

 which would necessitate its forming another aperture. Analogous 

 instances among the Clausiliae and Helicidae are much more common. 



The young are strongly and sharply sculptured, and have an elong- 

 ated spire. A correspondent in Science Gossip (May 1890) writes: 



" Periwinkles thrive remarkably well in my vases. I have had the 

 same individuals for ten years, and they breed freely. They must be 

 long-lived creatures, for they seem to grow very slowly. The young 

 ones are at first quite unlike their parents, and it is three years before 

 they begin to assume anything like the form of a 'winkle.'" 



Rissoa Frem. — Notwithstanding the expositions given by Jeffreys 2 

 regarding the admissibility of certain genera of this group of mollusca, 

 some writers still treat them seriously as generic. It is no doubt 



Crag Moll., vol. 3, p. 79, pi. v., . 10 a b. 

 British Conchology, vol. 4, pp. 3, 4. 



