NORTH PACIFIC OPHIURANS IN NATIONAL MUSEUM — CLARK. 105 



larger, swollen, wider than long, oblong with rounded corners, becom- 

 ing triangular, all well separated from each other. Side-arm plates 

 swollen, not meeting above or below, at least on basal half of arm; 

 each plate carries four well developed, thick, blunt arm spines; up- 

 permost, longest, rather more than half as long as joint; lowest, close 

 to tentacle pore and apparently functioning as a tentacle scale. Oral 

 tentacle pores provided with a very long, stout and conspicuous ten- 

 tacle scale on outer side; inner side protected by a conspicuous 

 median projection between the two pores. Tentacle pores of arm 

 round and conspicuous, but with no tentacle scales. Color (dried 



Fig. :i9.— Ophiopenia tetracantha. x8. a, from above; 6, from below; c, side view of three 



ARM JOINTS near disk. 



from alcohol), dull purplish brown or less commonly light yellowish- 

 brown. 



Localities. — Albatross station 2854, off Alaska, lat. 56° 55' N.; long. 

 153° 4' W., 60 fathoms, black sand, bottom temperature 42.8°, 2 

 specimens; station 3279, Bering Sea, lat. 56° 25' 40" N.; long. 162° 

 39' 15" W., 41 fathoms, fine gray sand, bottom temperature 37°, 1 

 specimen. Captains Harbor, Unalaska, 9 to 14 fathoms, 5 specimens; 

 same harbor, 60 to 80 fathoms, 2 specimens; Port Levasheff, 3 speci- 

 mens; W. of Amaknak Island, 60 fathoms, 7 specimens; Chagafka 

 cove, Kadiak, 12 to 20 fathoms, 330 specimens; Nazan Bay, Atka, 

 38 specimens; between Icy Cape and Cape Krusenstern, 1 specimen. 

 Bathymetrical range, 12 to 80 fathoms. Temperature range 42.8° to 

 37°. Three hundred and eighty-nine specimens. 



Type.— Csit. No. 25597, U.S.N.M., from station 3279. 



Although this species occurs in the same locality, and sometimes 

 even at the same station, as the preceding, it can not be confused with 

 it, for the two may be distinguished at once by the difference in the 

 arm spines. Even the smallest specimen of tetracantha, with a disk 

 diameter of only 3 mm., has four spines on one joint, three on the 



