112 GEOGEAPHICAL DISTRIBUTION. 



correspondence manifests itself among both the regular and irregu- 

 lar forms. In their bathymetrical distribution the echinoids appear 

 to be governed by much the same conditions as have been observed 

 in the case of the brittle-stars. By far the greater number of spe- 

 cies about two hundred are of a littoral habit, occupying the 

 belt of one hundred to one hundred and fifty fathoms, although not 

 a few of them, like Echinocardium Australe, which descends to 

 two thousand six hundred and seventy-five fathoms, penetrate deep 

 into the abyssal zone. The number of continental species, or such 

 whose normal habitat is included approximately between the one 

 hundred to one hundred and fifty and the five hundred fathom line 

 is forty-six, and a slightly larger number, fifty, may be considered 

 to be strictly abyssal. The species passing below two thousand 

 fathoms are rather limited, and only one is known Pourtalesia 

 laguncula whose range embraces the twenty- nine hundred fathom 

 line. This form is also found in the continental belt. 39 



The sea-cucumbers, or holothurians, which are very generally 

 distributed throughout the oceanic abyss, constitute one of the 

 most distinctive elements of the deep-sea fauna. As has already 

 been seen, they, together with certain annelids, form a large part 

 of the fauna of the "red clay," or of the region which lies beyond 

 the reach of foraminiferal shells. 



Deep-sea crustaceans are very abundant, and many of them are 

 remarkable for their colossal size, their bizarre forms (Nematocar- 

 cinus gracilipes), and brilliant red coloring. Partaking of the first 

 character are the giant blood-red shrimps of the genus Aristaeus, 

 and several members of the order Schizopoda. A Gnathophausia 

 was obtained off the Azores, by the officers of the "Talisman," 

 measuring no less than twenty-five centimetres (nearly ten inches) 

 in length. The peneid and caridid shrimps, among the long-tailed 

 decapods, are strikingly numerous, and present many very singular 

 forms. It would seem, from the observations of the "Challenger," 

 that the Brachyura, or crabs, were confined almost entirely to com- 

 paratively shallow water, although at depths of one thousand to 

 fifteen hundred fathoms they appear to have yielded a sufficient 

 harvest to the naturalists of the French expedition. Hermit-crabs 

 were collected by the " Talisman " in water of from four thousand to 

 five thousand metres. 40 Many of the pedunculated barnacles are of 

 uncommonly large size, surpassing in this respect the shallow-water 



