NOETH PACIFIC OPHIURANS IN NATIONAL MUSEUM CLARK. 17 



The rest of the collection, about one-fourth of the species, is made 

 up of forms with remarkable temperature ranges. The following 

 species have ranges of 20° or more: 



Ophiura sarsii, from 50.1° to 30.1°, a range of 20°. 



Ophiomusium h/mani, from 56.3° to 35.3°, a range of 21°. 



Oj^hiopholis aculeata (var. japonica), from 57.8° to 30.4°, a range of 27.4°. 



Amphiura diomedex, from 68.7° to 34.9°, a range of 33.8°. 



AmpModia euryaspis, from 58° to 32.7°, a range of 25.3°. 



Ophiacantha peniagona, from 62.1° to 36.4°, a range of 25.7°. 



Ophiacaniha normani, from 55.9° to 30.9°, a range of 25°. 



Ophiothrix koreana, from 68.7° to 42.5°, a range of 26.2°. 



Gorgonocephalus caryi, from 60.6° to 30.7°, a range of 29.9°. 



It is interesting to note that seven of these nine species belong to 

 the Oceanic fauna, as might have been expected, while the other 

 two are typical examples of the Honshu fauna. Of the remaining 

 eleven species of the Oceanic fauna, six have a temperature range of 

 more than 10°, while in four it is 3° or less; in Amphiura carchara, 

 which has the enormous bathymetrical range of over 1,900 fathoms, 

 the temperature range is only 7.8°, from 42.8° to 35°. Probably in 

 this species the bathymetrical range is determined by the temperature 

 rather than by any other factor. 



It is clear that the Oceanic fauna contains two quite distinct ele- 

 ments: One, which we may call group A, and which is much the larger 

 (thirteen species), is made up of forms to which temperature is a sec- 

 ondary factor, and a second, which we will call B, whose wide dis- 

 tribution seems to be due to the uniformly low temperature of deep 

 water. We have already seen (p. 14) that all the stricth^ deep-water 

 species (i. e., those not occurring in less than 300 fathoms) have a 

 very restricted temperature range, and of course the more abyssal the 

 habitat the more restricted is the temperature range. Although in 

 the present state of our knowledge, group B is only a small part (five- 

 eighteenths) of the Oceanic fauna, it is very probable that all the 

 strictly deep-water species really belong to that fauna, and should not, 

 simply because of their geographical habitat, be placed in the Honshu 

 or Bering or American faunas. If such a redistribution of the species 

 were made, group A would certainly prove to be the less important 

 half of the Oceanic fauna. 



ASSOCIATIONAL DISTRIBUTION. 



One of the most interesting phases of the study of a large collection 

 of any group of animals from a limited region is the determination of 

 what species occur together at any given station or in any restricted 

 area. Particularly interesting is it to note whether closely related 

 species occur together or in adjoining areas or are widely separated 

 from each other. We may approach the matter in two ways; first, 

 34916°— Bull. 75—11 2 



