NORTH PACIFIC OPHIURANS IN NATIONAL MUSEUM CLARK. 23 



There are only four genera represented which can be considered as 

 characteristic of deep water. 



5. The distribution of the deep-water species confirms the view 

 that species with a great bathymetrical range tend to become widely 

 distributed. 



6. The bathymetrical range of the species in the Oceanic fauna 

 confirms the view that species occurring on both sides of the North 

 Pacific have a great bathymetrical range. 



7. Although only one-sixth of the species are deep-water forms 

 and less than one-third belong to the Bering and Oceanic faunas com- 

 bined, nearly two-fifths of the species are distinctly cold-water 

 forms, occurring only in water under 45 F. 



8. Two groups of species combine to form the Oceanic fauna: 



A, composed of hardy species, with great temperature ranges, 

 to whom the temperature of the water seems to be relatively 

 unimportant, and 



B, composed of species to whom a uniformly low temperature 

 appears to be essential. 



9. There seems to be abundant evidence that very closely related 

 species of Ophiurans, often the most closely related, inhabit the same 

 area and that " Jordan's law" does not apply to this class of Echino- 

 derms. 



10. There is evidence that " physiological isolation" in some form 

 has been a more important factor than geographical or bathymetrical 

 isolation in the specific differentiation of Ophiurans. 



DESCRIPTIONS OF SPECIES. 

 Family OPHIODERMATID^. 



PECTINURAo ANCHISTA, new species. & 



Disk 14 mm. in diameter; arms 70 mm. long. Disk rather pentago- 

 nal, closely and completely covered by a fine granulation (about 80 

 grains to a square millimeter) , which even conceals the radial shields. 

 Upper arm plates tetragonal and broadly in contact on basal half of 

 arm, but on terminal half becoming triangular and finally well sepa- 

 rated from each other; at first they are much wider than long, even 

 twice as wide, but they ultimately are longer than wide; lateral mar- 

 gins, at first nearly parallel, gradually diverge distally, proximal mar- 

 gin becoming shorter and shorter, until at last it is obliterated. In- 

 terbrachial spaces below covered, like disk, by a fine granulation. 

 Genital slits moderate, about as long as three arm joints. Oral 



a For a revision of Pectinura and allied genera see Clark, Bull. Mus. Comp. Zool., 

 vol. 52, 1909, pp. 111-132. 



& "Arxtarof, signifying next or nearest, in reference to its close relationship to P. 

 cylindrica (Hutton). 



