Mr. Jeffreys on the Comparative Size of Marine Mollusca. 199 



14. Littorina rudis. This species is known to be extremely 

 variable in respect of size. The largest I have ever seen were 

 from the north of Ireland. 



15. Scalaria communis. I have never seen any Mediterranean 

 specimens equal in size to those found in this country. 



16. Bulla hydatis. Does Mr. M 'Andrew mean the B. hydatis 

 of Linnaeus, which is extremely rare in this country, but common 

 in the Mediterranean, or B. cornea of Lamarck, which is our 

 common species, though it is also found in the Mediterranean ? 



17. Murex erinaceus. British specimens are considerably 

 larger than those from the coasts of Spain collected by Mr. 

 M f Andrew, and now in the British Museum. 



18. Cerithium reticulatum. Mr. M f Andrew probably means 

 the large variety (C. lima of Bruguiere), which is found in the 

 Channel Isles as well as in the Mediterranean. Specimens of 

 the normal form, which I obtained by dredging on the Pied- 

 montese coast, are smaller than those of our own shores. This 

 last is the var. /8. of Philippi. 



19. Cerithium (Triforis) perversum. The same remark applies 

 to this also. 



20. Aclis supranitida. Specimens collected by myself in 

 North Wales are quite as large as those of Mr. M f Andrew from 

 Madeira. An allied species (A. ascaris)j which is of a much 

 smaller size, is frequently confounded with the above, and may 

 have been referred to by Mr. M 'Andrew as the British species. 



Tellina balaustina is not, as Mr. M 'Andrew might lead your 

 readers to suppose, only found on the western or Atlantic coast. 

 It also occurs on the eastern coast of Zetland, and probably is 

 as common there as in the Mediterranean; but the northern 

 seas are, during the greater part of the year, too stormy to admit 

 of much exploration. 



Even in the case of the Teredines, which inhabit submerged 

 and floating wood, and may therefore be supposed to be peculiarly 

 subject to climatal influence, specimens of Teredo denticulata 

 from Greenland, in the British Museum, are twice the size of 

 the few specimens which have been hitherto found living on 

 the British shores ; while T. Philippii attains here much greater 

 dimensions than in Sicily or more southern parts. British 

 examples of J 7 . Norvagica, T. navalis, and T. pedicellata, appear 

 also to exceed in size those found on the north coast of Spain 

 and in Sicily, judging from the figures given by Quatrefages 

 and Philippi. The Teredines are stated by M. Laurent not to 

 be pelagic, but confined to the coast-line, although some of the 

 species have a very wide geographical range. 



Taking the British Mollusca as the standard of comparison, I 

 would also remark that the following species in particular appear 



