Atigust 1 6, 1877] 



NATURE 



325 



The species named in the above list are 75 in number. Of 

 these no less than 46 have been described by me for the first 

 time in the Annals and Magazine of Natural History, for 

 1876 and 1877. Several of them were also procured in the 

 Porcupine; Challenger, and X'dringen expeditions. A great many 

 more deep-sea species remain to be worked out and described by 

 me from the Porcuputc expeditions of 1S69 and 1870. 



I have not included the pteropods in the list, although their 

 shells occur at the greatest depths — because they are oceanic, 

 and inhabit only the surface or superficial zone, their shells 

 falling to the bottom after death and when evacuated by pre- 

 daceous animals. ^ 



The moUusca of very deep water, or the benthal zone, are 

 certainly peculiar, and constitute part of a distinct fauna, 

 notwithstanding that some of them frequent shallower water. 

 It is very difficult to say how far they may be affected by 

 bathymetrical conditions. An important contribution to this 

 part of the subject was made by Mr. Buchanan at a recent 

 meeting of the Royal Society of Edinburgh, in which he stated, 

 as the pi eliminary result of his analysis of the sea- water collected 

 in the Challenger expedition, that as regards the percentage of 

 oxygen present at different depths, it diminishes from the surface 

 to a depth of 300 fathoms, and increases from this point to lower 

 depths.' See also my account of the behaviour of Trochus occi- 

 dtntalis, when dredged from the deep-sea zone on our northern 

 coasts, which is explained by Mr. Buchanan's statement.'' 



They are not .always of a small size. In the Poreupine expe- 

 dition of 1S69, the dredge brought up, at the depth of 1,207 

 fathoms, in the Bay of Biscay, a living specimen of Fiisus 

 nttenuctus, which measures two inches and a quarter in length ; 

 and another dredging at the depth of 2,435 fathoms (nearly 

 three miles) in the same part of the Bay, yielded a living specimen 

 of Dentiiliuni candidum about an inch and a half long. In the 

 C/;a//e'«5'(7- expedition was trawled, at the depth of i , 600 fathoms, 

 in the South Atlantic (S. Lat. 46* 16', E. Long. 48° 27'), a living 

 specimen of a magnificent shell belonging to Cyinbiiim or an 

 allied genus, which has a length of six inches and three-quarters 

 and a breadth of four inches ! And during my cruise in the 

 Valorous, I dredged, at the depth of 1,100 fathoms, in Davis 

 Strait, a living specimen of Dentalium candidum an inch and 

 thre -quarters long. These treasures of the deep are so apt to 

 entrance the imagination of a naturalist, that I have often dreamt 

 of walking on the sea-bed and picking up unknown and won- 

 derful shells ; and in my waking hours I have envied the faculty 

 of the argonaut in Morris's " Life and Death of Jason," 



I hope it is pardonable to avail one's self of a little poetical 

 licence to make the quotation applicable to the bottom as well 

 as to the surface of the sea. 



The distribution of thi. deep-sea moUusca is unquestionably 

 caused by submarine currents, with the direction and extent of 

 which, however, we are unacfjuainted. As far as I have had an 

 opportunity of judging from the moUusca of the North and 

 .South Atlantic, I atn inclined to think that the Arctic and Ant- 

 arctic currents do not extend beyond the Equator. The South- 

 Atlantic species procured by the Challeni>er party in deep water 

 appear to be different from those of the North-Atlantic in similar 

 depths, according to our present notion of species. It is un- 

 necessary for me to renew my objection to the phrase " repre- 

 sentative species," as Sir Wyville Thompson has satisfactorily 

 disposed of the matter in page 14 of his " Depths of the Sea." 



It will be seen, on referring to the list of deep-water moUusca 

 procured in the Valorous cruise, that several of the species are 

 also SiciUan fossils. They occur in the Pliocene formation of 

 the south of Italy. Professor Seguenza has just published a very 

 complete and valuable catalogue entitled " Elenco dei Cirripedi 

 e dei MoUuschi della zona superiore dell' antico plioceno,' which 

 are arranged in two divisions, " Depositi littorali " and " De- 

 positi submarini." But some further distinction would seem to 

 be necessary in order to separate the strata, inasmuch as certain 

 species which are assuredly littoral are included in the submarine 

 division. For instance, Acttion pusillus, Forb. (which lives at 

 depths varying from 40 to 1,456 fathoms), and Cylichna oiiata, 

 J. (66-862 fathoms), are entered in both divisions ; while pecu- 

 liar:^' shallow- water species, such as Patella vulgata, Tectura 

 virginea, and six now also living species of Chiton, appear only 

 in the submarine or deep-water division. Many of the species 



vIatube, June 14, 1877. 

 ' British Conchology," vol. 



• PP- 335, 336. 



in Seguenza's Catalogue (besides those noticed in the Valorous 

 list of deep-water moUusca), which had been previously con- 

 sidered extinct, were discovered by me in the Porcupine expe- 

 ditions to be still living ; and I have no doubt that the rest of 

 the so-called extinct species, from the upper zone of the older 

 Pliocene in Sicily, wiU sooner or later be detected in future 

 deep-sea explorations. In fact our examination of the abyssal 

 fauna has been hitherto extremely slight and cursory, taking into 

 account the enormous extent of area, the difficulties caused by 

 unfavourable weather, and the inadequacy of the instruments 

 used in the investigation. Our good neighbours, the Norwegians, 

 have not relaxed in their work ; and while this Address is being 

 delivered their second year's expedition to the Arctic seas will 

 almost have been completed. May every success attend them ! 



There has been lately a good deal of controversy as to the 

 supposed " continuity of the chalk " ; and the affirmative of the 

 proposition has been most ably argued by my colleague and 

 friend. Sir Wyville Thomson, in his " Depths of the Sea." 



Prof. E. Forbes, in his" Report on /Egeanlnvertebrata"( 1844), 

 was, I believe, the first to state the proposition. He says, at p. 

 178, that the strata in his lowest region, or 230 fathoms, would, 

 if filled up, "present throughout an uniform mineral character 

 closely resembling that of chalk, and will be found charged 

 with characteristic organic remains and abounding in foramini- 

 fera. We shall, in fact, have an antitype of the chalk." 



Sir Wyville Thomson supports his view by the weighty autho- 

 rity of Dr. Carpenter, Prof. Huxley, and Prof. Prestwich ; and 

 although the late Sir Charles L^ell entered a vigorous protest 

 against the hypothesis, and went so far as to designate it a 

 " popular error," I will refrain from expressing any opinion of 

 my own, but will content myself with stating a few facts in 

 elucidation of the question. 



The comparison of the deep-sea ooze with the geological 

 formaiion known as chalk depends on two points, viz., the 

 mineral composition and the organisms belonging to each. 



1 . Mineral Composdion. — The late Prof. David Forbes, whose 

 knowledge as a mineralogist and chemist was universally recog- 

 nized, furnished me, on my return from the Porcupine expedition 

 of 1S69, with a complete analysis of a sample of Atlantic mud 

 procured at a depth of 1,443 fathoms. He proved that it differed 

 from ordinary chalk in containing scarcely more than 50 per 

 cent, of carbonate of lime, whereas chalk consisted all but 

 entirely of carbonate of lime. Indeed Sir Wyville Thompson 

 admits that "a more careful investigation shows that there are 

 very important differences between them." 



2. Orgmnisms. — I must here confine myself chiefly to the 

 moUusca, which Sir C. LyeU regarded as " the highest or most 

 specialized organization " on which geological reasoning and 

 classification are founded. 



Misled by the apparent resemblance of Mediterranean and 

 Atlantic ooze to the ancient chalk, geologists have been accus- 

 tomed to consider the chalk fauna as having lived in deep water. 

 Let us see how this is with respect to the moUusca. I have 

 lately, with the assistance of Mr. Henry Woodward and Mr. 

 Etheridge, examined the cretaceous moUusca in the British 

 Museum and the Museum of Economic Geology ; and Mr. 

 Etheridge has most obligingly prepared and furnished me with a 

 tabular list of the genera and number of species in each genus iu 

 the upper cretaceous group (exclusive of the gault and green- 

 sand), which list I will, with his permission, here insert : — 



Brachiopoda. 



Argiope 



Crania 



Kingena ... 



Magas 



Rhynchonella 



Terebratella 



Terebratula 



Terebratulina 



Telebrirostra 



Thecidea ... 



Trigonosemus 



Total 



No. of 

 species in 



No. of 

 species in 



