DEEP-SEA FAUNA. 247 
sublittoral or intermediate depths, while the most highly specialized forms 
are more characteristic of the very shallow waters. Such is the case with the 
Paguridx.* 
Doubtless in certain groups of lowly organized animals many species cast 
in the antique mould survive in the abyssal depths of the ocean. But in 
highly specialized groups, like the Stalk-eyed Crustacea, — beings endowed 
with visual and respiratory organs of a very perfect grade, —the peculiar 
conditions that surround the dwellers of the deep work great structural 
changes. Correlated with the retrogression of the visual organs, marked 
changes take place affecting the antenne and anterior parts of the body 
generally. The purity of the water in these still regions often leads to a 
more or less complete disappearance of the epipods or “ gill-scrapers.” 
So it comes about that the Crustacea living at a great depth are apt to 
be rather specialized types, — further removed from the primitive ancestral 
stock than are the allied species of the shore. Taking the animal kingdom 
as a whole, it is probable that the archaic forms now extant in the shallow 
waters of the land or coast, or in the moderate depths below the strictly 
littoral zone, far outnumber those surviving in the extreme depths of the 
sea. Heterodonta, the Ganoid fishes, Limulus, Pollicipes, Trigonia, and Lin- 
gula are all peculiar to shoal water. So are the Unionide of the rivers and 
ponds. Nautilus and Pleurotomaria come from very moderate depths. The 
Brachiopods, distributed from the shore-line to 2945 fathoms, attain their 
maximum development in from 50 to 250 fathoms. The wonderful Crinoid 
fields, — those lily beds of the Caribbean Sea, — lie at a depth of but 50 to 
200 fathoms beneath the surface. 
Only in a very broad and general sense may the deep-sea Crustacea, 
taken as a whole, be called antique types, inasmuch as they are to a very 
great degree members of the Anomuran or Macruran series, — low in the 
scale of classification, and in so far more primitive forms. Only four species 
(representing two genera) of Brachyura were discovered by the “ Albatross” 
below 500 fathoms,t and these low in the Brachyuran scale. As bearing on 
the suggestion of the boreal origin of the deep-sea Crustacea, it may be 
observed that the Brachyura, that great group which scarcely tinges the 
* Milne Edwards and Bouvier, in Ann. Sci. Nat., Zool., 7 ™? Sér., XIII. 195, 1892; Mem. Mus. Comp. 
Zool., Vol. XIV., No. 3, p. 9, 1893. 
+ In the vast amount of material obtained by the “Challenger” during the cireumnavigation of the 
globe only four species (belonging to three genera) of Brachyura came from below 500 fathoms. ‘Two of these 
are the same as two of the four species secured by the ‘“ Albatross” below the 500 fathom line. 
