76 



BULLETIN 75, UNITED STATES NATIONAL MUSEUM. 



56.3°, 3 specimens; station 5094,Uraga Strait, Japan, lat. 35° 4' 42" N. ; 

 long. 139° 38' 20" E., 88 fathoms, black sand, broken shells, bottom 

 temperature 54.8°, 5 specimens; locality (?), 2 specimens. Bathy- 

 metrical range, 57 to 191 fathoms. Temperature range, 56.6° to 42.5°. 

 One hundred and five specimens. 



This fine series of specimens, the disk diameters of which range 

 from 6 to 20 mm., shows conclusively that the original specimens, 

 on which the species was based, were immature. It has therefore 

 seemed advisable to give figures of the adult. The only impor- 

 tant changes which take place as the individuals increase from a 

 disk diameter of 7 mm. to one of 20 are found in the arm comb and 

 the arm spines. The change in the arm comb is an increase in the 



Fig. 22.— Ophiura sterea. x2.5. a, from above; 6, fro.m below; c , side view of base of arm. 



number of papilla?, of which there may be as many as twenty-five. 

 The change in the arm spines is far more important; the number of 

 what we may call true arm spines changes little, for there are usu- 

 ally four or five, and only rarely six, but there develops on the 

 distal margin of the side arm plates a secondary series of spines, 

 which may be quite conspicuous, and consist of as many as fifteen 

 spinelets. These spinelets are usually flatter, thinner, and more trun- 

 cate than the true spines, but while the differences may be marked, 

 it is often difficult to distinguish between the true and the secondary 

 spines. This is particularly so at the base of the arm, as may be 

 seen in fig. 22c. On the whole, sterea seems to be very well character- 

 ized and quite distinct from any of its nearest relatives. 



