62 MAIOTAL OF THE MOLLTJSCA. 



herring-fisheries) is essentially Atlantic ; many of the species 

 are of ancient origin, and occur fossil in the Pliocene. 



The British moUusca described by Porbes and Hanley amount 

 to 682, viz. :— 



14 (15) Cephalopoda. 100 Pulmonifera. 175 (172) Acephala, 



220 (254) Marine Univalves. 4 (5) Pteropoda. 73 (73) Tunicata. 



91 (100) Nudibranchiata. 6 (7) Brachiopoda. 



Of this number two-thirds of the Nudibranchia, 55 marine uni- 

 valves, and 7 bivalve shell-fish, are, at present, only known in 

 British seas; but as most of these are minute or ''critical" 

 species, it is considered they will yet be met with elsewhere. 

 In 1857, Mr. M'Andrew was acquainted with 626 marine mol- 

 luscs, as indicated by the figures in brackets in the summary 

 just given. 



A few of the species belong to the Lusitanian province, whose 

 northern limits include the Channel Islands, and just impinge 

 upon our coast. 



PhasiancUa puflus. Miirex corallinus. Cytherea chione. 



Haliotis tuberculata. Avicula Tarentina. Petricola litliophaga. 



TruncateUa Montagui. Galeomma Turtoni. Venerupis irus, 



Oncidium celticum. Pandora rostxata. Cardium rusticum, L. (tnber- 



Bullahydatis. Ervllia castanea. culatum). 



Volva patula. Mactra helvacea. 



Of the Gasteropoda 54 are common to the seas both north and 

 south of Britain ; 52 range farther south, but are not found 

 northward of these islands ; and 34 which find here their south- 

 ern limit occur not only in Northern Europe, but most of them 

 in Boreal America. Nearly half of the bivalves range both 

 north and south of Britain; 40 extend southward only, and 

 about as many more are found in Scandinavia, 27 of them bemg 

 common to N. America. {Fortes.) 



In the lists of Arctic and Boreal shells the British species are 

 distinguished by an asterisk. 



According to Mr. M 'Andrew's estimate in 1850, 406 British 

 shell-bearing moUusca were then known, of which 



217 or 53 per cent, were common to Scandinavia. 

 246 or 61 „ „ North of Spain. 



227 or 66 „ „ S. Spain and Medit. 



97 or 24 „ „ Canary Islands. 



G-. Jeffreys. The Nudibranchiata alone have been more fully described in the 

 publications of the Ray Society, by Messrs. Alder and Hancock. For the marine 

 zoology of the coasts of Denmark the " Zoologia Danica " of 0, P. Miiller is still the 

 most important work. 



