114 BATHYMETRICAL DISTRIBUTION OF MARINE MOLLUSKS. 



noi^th, quite a number being moreover common to Europe. These 

 two regions are sometimes treated of together as the Pennsyl- 

 vanian province. 



I have already stated in treating of the Boreal Province that 

 the barrier of Cape Cod has not influenced the distribution of 

 the mollusca nearly so much as was formerly supposed ; that 

 some southern forms surmount it, and that many northern forms 

 extend further southwards. On the other hand, the Gulf Stream 

 has exercised a wonderful influence upon the fauna of the 

 Southern shores of the United States, as far northwards as 

 Fort Macon, JST. Carolina, adding many semitropical forms to 

 our mollusca. 



Crepidula, Fulgur, large species of Venus and of Mactra are 

 among the characteristic shells of a region which possesses but 

 little claim to the title of a distinct province. Lingula, one of 

 the most ancient of genera, is now nearly confined to the Austra- 

 lian and Philippine seas ; yet a peculiar species is found in the 

 waters of North Carolina ; and not only a Dolium, but a new 

 Pholadomya, the second living species of that ancient group 

 have been recently dredged b}^ Yerrill in New England waters. 

 Liltorina litorea is a comparatively recent importation from 

 northern Europe. It was first detected, a few 3^ears since on the 

 Nova Scotia coast, where it had probably arrived on ballast ; we 

 next hear of it as somewhat plentiful around Boston, and it has 

 now spread south westwards, as far as New Haven, Conn. 

 The writer found it, in the summer of 1881, the most plentiful 

 moUusk on the rocky coasts of Newport, R. I. 



BATHYMETRICAL DISTRIBUTION OF MARINE MOLLUSKS. 



The distribution of marine animals according to depth is 

 subject to laws quite as evident as those which govern their 

 geographical distribution. Messrs. Andouin and Milne-Edwards 

 (1830), M. Sars (1835), (Ersted (1844), Forbes (1841-2), have 

 studied this subject, and proposed schemes of bathymetrical 

 classification, all founded upon the supposition that the existence 

 of animal life at considerable depths was impossible. Of late 

 years four zones or vertical regions have been recognized ; and 

 the deep-sea dred^ings of the past fifteen j^ears (having fully 

 demonstrated the existence of life at vast depths, a fifth zone 

 may now be added. 



The dredging expeditions which have established the above 

 highly interesting fact, and so largely increased our knowledge 

 of the distribution of the Mollusca are : American, those of the 

 Gorwin (1867), Bibb 0808-1869), Blake (1877-1878), Fish 

 Hawk (1880-1881) ; English, Lightning (1868), Porcupine (1869- 

 1870), C/i.aZ/enger (1873-1876), Valorous (1875); Scandinavian, 



