NOBTH PACIFIC OPHIURANS IN NATIONAL MUSEUM CLARK. 



61 



11 specimens. Bathymetrical range, 70 to 876 fathoms. Tempera- 

 ture range, 56.3 to 36.5. One hundred and seventy-six specimens. 

 These specimens show a most remarkable difference in the calcifi- 

 cation of the disk, for while several of them have the disk covering 

 thick, with the scales hardly distinguishable, as in Lyman's type, 

 others have it much thinner with the scales evident, while still 

 others have a greater or less part of the disk covered by a flaked 

 skin, the calcification being confined to the vicinity of the radial 

 shields and to the interradial margins. The gradation between the 

 two extremes is so complete that there can be no doubt that the 

 amount of calcification is an individual and not a specific or even a 

 local matter. Thus the specimen from station 5094 has the disk 

 fully calcified, while of two 

 specimens from station 

 5093, one has the center 

 of the disk bare with ten 

 bare lines running out into 

 the radii and interradii, 

 and the other has the disk 

 completely lacking calcifi- 

 cation save about the mar- 

 gin and the radial shields. 

 That it is not a matter of 

 age would seem to be in- 

 dicated by the fact that 

 the largest (disk diameter, 

 26 mm.) and one of the 

 smallest (disk diameter, 

 9 mm.) specimens have 

 less calcification than any 

 others. Considerable di- 



Versity is shown also in the FIG- 15. OPHIURA FLAGELLATA, YOUNG. X6. a, FROM ABOVK; 

 length Of the arm spines, 6 > FROMBEI <: c, sn> E VIEW OFTWO ARM JOINTS NEAR DISK. 



in the form of the radial 'shields and in the number of tentacle scales, 

 but these differences do not seem to be correlated in any definite way 

 with the amount of calcification. The form of the radial shields, 

 arm plates, and arm spines, the number of the latter (three) and the 

 arm comb appear to be very constant features in mature specimens. 

 In young individuals (see fig. 15) both the upper and under arm 

 plates are much longer and narrower than in adults, and some- 

 times the side arm plates do not quite meet below, though the under 

 arm plates are widely separated nevertheless. The comb papillae 

 are much longer and more slender than Lyman's figure a indicates. 



a Challenger Oph., 1881, pi. 4, fig. 17. 



