298 Mr. Jeffreys on new Species of Mollusca. 



had ventured to suggest on former occasions with respect to the geo- 

 graphical distribution of the marine fauna of Europe. A yachting 

 excursion which he had taken in the course of this summer, accom- 

 panied by two scientific friends, to the northernmost part of the British 

 Isles, together with an examination of the upper tertiaries in Suffolk 

 and Norfolk which he had since made in company with Mr. Prest- 

 wich, gave the author a better insight into the scope of such distri- 

 bution than had resulted from his previous researches, and confirmed 

 his belief that the division into separate areas or " provinces," which 

 had been proposed by so many systematists (all of whom held differ- 

 ent opinions as to the extent and limits of such "provinces"), was 

 erroneous, and that the present distribution must be referred to a 

 state of things which has indeed passed away, but left a very distinct 

 impress of its action. The author is inclined to take the Coral- 

 line Crag as a starting-point, and to consider the marine fauna of 

 Europe, Northern Asia, the Cis-Atlautic zone of Africa, and part of 

 North America, as having been closely related at a comparatively 

 recent epoch, and as forming one common area of origin. Many 

 species of Mollusca once existed at both extremities of this vast di- 

 strict : e.g. Mya truncata and Buccinum undatum; and other species 

 hitherto supposed to be restricted to the Mediterranean (viz. Mono- 

 donta limbata and Cerithium vulgatum, with its variety C. calabrum) 

 have lately been discovered by Professor Sars on the coasts of Fin- 

 mark. It is also probable that the recent exploration of the Green- 

 land seas by Otto Torell and others may reveal further instances 

 of a similar kind. Very little has hitherto been done towards the 

 investigation of the Arctic fauna. It by no means follows that an 

 extremely rigorous or " arctic " temperature prevailed in those 

 places where we find the remains of some mollusca which now inhabit 

 only the seas of colder regions, or vice versa that the presence in these 

 regions of fossil shells belonging to species which now inhabit only 

 more southern seas indicates the former prevalence of a warm climate. 

 The temperature of the sea at certain depths is well known to be very 

 ecmable ; and it is only littoral or shallow-water species that would 

 be exterminated or affected by a change of climate. Some kinds ap- 

 pear to be more hardy than others, and to have survived consider- 

 able and perhaps frequent changes of temperature ; while others have 

 undergone a limited modification of form, and are considered by some 

 naturalists as distinct (or "representative") species. A great deal, 

 however, yet remains to be done, by accumulating facts, and a criti- 

 cal comparison of recent with fossil species, before a complete or 

 satisfactory theory of distribution can be established. 



Mr. Jeffreys contrasted his experience of this dredging expedition 

 with those he had made to other parts of the British coasts as well 

 as to the Mediterranean, and also with the accounts he had received 

 of similar expeditions to the coasts of Norway and Sweden — showing 

 the far greater difficulties which attended an exploration of our 

 northernmost sea, by reason of the variable and often tempestuous 

 weather, and of that line of coast being unsheltered from the pre- 

 vailing winds. He, however, succeeded in procuring three species 



