From J. D. Dana   8 September 1856

My dear Sir:—

I received your most welcome letter a few days before the meeting of our Scientific Association:¹ and as I should meet Prof. Agassiz² there, who could best answer your queries respecting the Mammoth Cave Animals, I concluded to defer my answer till my return. Here I am, back again, at last and I seat myself for a few words with you, socially and Scientifically.—

First as to the Mammoth Cave.— Professor Agassiz told me that the family to which the Fishes belong—the Cyprinodonts—was rather strikingly American.³ With regard to the Insects, Dr John L. LeConte an Excellent Entomologist says that the genera of beetles are not American, but the same that occur in Caverns in Europe & elsewhere.⁴ The genus of fly Anthomyia is common in Europe.⁵ The Crustacean, Astacus pellucidus, belongs to that subdivision of the genus, (Cambarus, as it has been called), which is peculiarly American. Cambarus is made a distinct genus by some writers: the only difference is in the number of branchiæ: Cambarus has 17, on a side or one less than Astacus.— The Crustacean genus Triura, has not been found any where except at the Mammoth Cave. You may have seen some notice of the species of the Cave in the Amer. Jour. Sci., vol. xi, p. 127 (1851).—⁶ Of the spiders I cannot speak definitely.— I would add respecting the genus Cambarus, that its Species are very numerous and widely spread over North America. Agassiz has collected a large amount of information on the peculiarities of the North American Fauna, but he has not yet embodied them in any work or article. One of the most interesting of our peculiar tribes, as you undoubtedly know, is that of the Gar-pikes, of which there are several genera & near two dozen known species occurring over the Continent between Cuba & the northern Lakes—and not represented elsewhere over the globe.— It is not to the point in view, yet I may mention here a fact of geological interest brought out by Agassiz at our Assoc. meeting a fortnight since. There were some young individuals, alive, shown, which had the tail of the Ancient Ganoids— That is, the vertebræ were actually continued to the extremity of the upper lobe—⁷ This upper lobe, as here drawn, drops off as the animal grows & the fish then is of the modern type of form.⁸

It was a striking illustration of the principle discussed by Agassiz—that the earliest species in Geological history often have relations to the early or embryonic forms of existing species.—⁹

With respect to Genera represented by both northern & Southern species and not by tropical:—¹⁰

There are several which may be as correctly considered northern as southern, or the reverse.

Lithodes is a cold water genus, found about the South Extremity of S. America, and also in the N. Atlantic & N. Pacific. There are 2 known northern species, & 4 Southern. Still I should doubt the propriety of calling it a Southern genus. There is also another closely related genus described by Adam White¹¹ called Echidnocerus found near the mouth of the Columbia R.— I have not seen the species

(The Genus Eurypodius of Southern S. America is represented in Puget’s Sound, by the Genus Oregonia (D.) differing but little.)

Cancer (Platycarcinus of Edw.) occurs about Britain, Eastern North America (northern part of the U.S.), also along the coast of Chili, and about New Zealand & Tasmania; but not in the Tropics. There are 5 species in the N. Temperate Zone, and as many in the South Temperate.

Atelecyclus is found about Britain (3 species), on the coast of Chili (1 sp.), and along Japan (1)   Peltarion is a closely related genus found at the Falkland’s.

Bernhardus, of the Paguridea, is represented quite largely in the North and South temperate zones and not in the warmer tropical zone, as far as known.

Homarus has two species in the North Atlantic, (one American & one European,) and one near Cape Town, in the South Atlantic.

Crangon is one of the northern genera not yet found south.

Portunus is eminently north temperate: but like Cancer, has species both in Britain, and in New Zealand & Tasmania; in no other parts of the globe as far as ascertained do these two genera occur together (see p. 1578 of my work)—¹² we may say that it is a northern genus, as the larger part of the known species are in the north. Yet it is possible that if there had been as much coastline in the South, there would have been as many Southern species. In such comparisons the amount of coast line—that is, the extent of possible habitats—is an important element.

I do not know that the facts here stated meet precisely the question you have under consideration: and if not, do not hesitate to put more enquiries, and I will do my best to answer them.— In my Chapter on the subject of Geog. Distribution I should not have used the word Kingdom as I have done.¹³ Some other term for the great sections of the globe would have been better.

You may have noticed that in citing the chapter in the Amer. Jour. Sci., I changed the name Nova Scotia Province, to Acadian Province¹⁴   I have always looked on my review of the Distrib. of Crustacea, as only a beginning, which the future would extend & correct—a first effort, as regards Crustacea, in a field that will yet afford great results. For want of a knowledge of the difference of temperature between the waters of the coasts of Europe & N. America Milne Edwards made poor work in his “Crustacés” (1834) in a chapter on the Distribution of Species;¹⁵ and for a like reason, naturalists generally had failed to appreciate the wide difference, in water & land distribution on the same coasts. It is something to know that the plants and birds may have equatorial heat, when the fishes of the neighboring waters are in the temperate zone: & this at least is clear from my survey of the subject.—

As to fossil trees in the South Shetland’s— D^r James Eights says (Transactions of the Albany Institute vol. ii, p. 64)¹⁶—(after describing the rocks of the Islands as basalt & a conglomerate, passing into a tufa (if I may judge from his description) and farther into “a fine argillaceous substance with an imperfect slaty structure and a Spanish-brown aspect” often containing zeolites especially near “the incumbent amygdaloid”)— “The only appearance of an organized remain that I any where saw, was a fragment of Carbonized wood, imbedded in this conglomerate. It was in a vertical position, about 2$\frac{1}{2}$ ft. in length and 4 inches in diameter   Its color is black, exhibiting a fine ligneous structure; the concentric circles are distinctly visible on its superior end; it occasionally gives sparks with steel and effervesces slightly in nitric acid.”—¹⁷

The part of your letter which afforded special pleasure was that alluding to your home group—¹⁸ I cannot speak of mine as “large”, yet I may as “good & happy”—Fanny the oldest 10 years—Edward, 6 (nearly 7) and James, 3.—¹⁹ I was also pleased to hear of Mr Lubbock’s happiness.²⁰ A long life to them full of joys.— Please thank him from me for the pamphlets which he has sent. He is doing excellent work among the Entomostracas,²¹ and dear little things they are.

—You query as to my whereabouts. My Professorship is here at New Haven where I have been living since the return of the Expl. Expedition after the first two years—in other words, since 1844—the year in which I was married at this place.

I have been interested recently in the “Embryogeny” of N. America, and before many months have past will send you a pamphlet on the subject.— That title sounds queer, yet is not inappropriate: I entitle the article “On the plan of development in the Geological History of N. America”—²² I have not space or time for explanations now and therefore must ask you to wait a little before you set me down as a mere speculator.

With warm wishes for your welfare, I remain | Sincerely your friend | James D. Dana

Ch. Darwin Esq.