118 Mr. R. M 'Andrew on the Comparative Size of Mollusca. 



nishing in size and frequency as we follow it along the coasts of 

 Nordlarid and Finmark, as well as to Gibraltar, its most southern 

 locality. The little A. triangularis I did not find in northern 

 Scandinavia : it is extremely abundant in some parts of the 

 Hebrides; but, though rare, is of larger size in Gibraltar Bay 

 than I have met with it elsewhere. I take this opportunity of 

 mentioning that I have recorded this species from the Canary 

 Islands ; but Mr. Searles Wood, to whom I showed them, be- 

 lieves the Canary specimens (smaller even than the British) to 

 be a different species, and identical with a Crag fossil. A. in- 

 crassata, a more southern species, is rather larger in the Canaries 

 than in the Mediterranean. 



The genus Crenella is analogous to that of Astarte. C. discors 

 and C. decussata attain larger growth and are more abundant in 

 the Arctic and Boreal regions than in the Celtic. C. marmorata, 

 which ranges from Finmark to the Canaries, is largest and most 

 frequent on the Scottish coast ; while the more southern form, 

 C. rhombea, is rather larger in the Canaries and Mediterranean 

 than at the northern limit of its range in the British Channel. 

 So with the genera Nucula and Cardium ; N. lavis, C. suecicum, and 

 C. fasciatum become smaller as we follow them southward from 

 their principal habitat in northern Scandinavia. N. nucleus is 

 as large at Gibraltar as in Finmark, being eminently a Celtic 

 species ; while of N. decussata my largest specimens are from 

 Malaga ; and C. rusticum becomes larger as we proceed south 

 from the British Channel, attains its maximum at Gibraltar, and 

 is smallest in the Canaries. C.papillosum is also largest in the 

 Mediterranean, though distributed both northward and south- 

 ward in the Atlantic. C. pygmaum is smaller in the Mediterra- 

 nean than in Britain, but I have obtained it largest in Vigo Bay. 



Venus verrucosa, like Cardium i*usticum, has its northern limit 

 in Britain, increases in size southward to Gibraltar and the 

 Mediterranean, and is again much smaller in the Canaries. 

 Mactra stultorum grows to larger size in Minorca than in Britain. 

 Of Fusus antiquus, ranging to within the Arctic Circle, the 

 largest specimens have been obtained in Liverpool Bay. Litto- 

 rina rudis attains as large growth upon the coast of the north of 

 Spain as upon that of Finmark. Scalaria Turtonis is larger in 

 Britain than in the Mediterranean or at Madeira. S. communis, 

 on the contrary, is larger at Gibraltar than in England. 



Bulla hydatis is very diminutive in the Mediterranean com- 

 pared with British specimens ; but those from Vigo (situated 

 south of the shores of Piedmont) are fully equal in size to the 

 British or Irish. 



Murex erinaceus grows larger upon the coasts of Spain, both 

 north and south, than in Britain. Cerithium reticulatum and 



