PRIONECHINUS DEPRESSUS. 309 



the test pale brown and the base of the spines tinged with olive, while the third 

 has the tubercles and the basal half of all the larger spines pale red. 



These specimens were taken at the following stations : — 



Station 4965. Between Kobe and Yokohama, Japan; 33° 35' 20" N., 

 135° 10' 50" E. Bott. temp. 49.4°. 191 fathoms. Dk. gn.-gy. s., sh. 



Station 4967. Between Kobe and Yokohama, Japan; 33° 25' 10" N., 

 135° 37' 20" E. Bott. temp. 45.9°. 244-253 fathoms. Br. m., s., for. 



Station 5086. Sagami Bay, Japan; 35° 8' 15" N., 139° 20' E. Bott. temp. 

 43.7°. 292 fathoms. Gn. m., crs. bk. s. 



Bathymetrical range, 191-292 fathoms. Extremes of temperature, 49.4°- 

 43.7°. 



Three specimens. 



Prionechinus depressus A. Ag. and CI. 



Prionechinus depressus A. Agassiz and Clark, 1907. Bull. M. C. Z., L, p. 244. 



Plate 101, figs. 1-3. 



The largest specimen of this species is 10 mm. in diameter but the height of 

 the test is hardly 4 mm. The abactinal system and actinostome are about 

 equal to each other, measuring 5 mm. across, which is practically the length of 

 the primary spines at the ambitus. There are 11 coronal plates in the inter- 

 ambulacral as well as in the ambulacral columns. In another specimen, 7.5 mm. 

 in diameter, the test is 3.5 mm. high, while in a still smaller one, 6.5 mm. h. d. 

 the vertical diameter is fully half the horizontal. The depressed test therefore 

 seems to be acquired with age. There is practically no sculpturing on the test 

 and very little, if any, on the genital plates (PI. 101, fig. 3). The genital pores 

 are at the extreme distal tips of the genital plates. The pore is placed in a notch 

 which is continuous with the sunken, median interambulacral suture, which 

 in this species is very marked clear to the ambitus, at least in specimens over 

 7 mm. h. d. The ambulacra are rather wide, decidedly more than half as wide 

 as the interambulacrum at the ambitus. The pores are larger and the porif- 

 erous areas wider than in specimens of sculptus of the same size. 



In all other particulars (tuberculation, character of actinostome (PI. 101, 

 fig. 2), spines, pedicellariae, and color) this species is so similar to sculptus as to 

 be practically indistinguishable. The difference in the genital pores is very 

 noticeable and in large specimens the shape of the test affords an obvious means 

 of distinction. An examination of the reproductive organs fails to show that the 



