86 OPHIOCOMA ERINACEUS. 



placed. Teeth stout, thickened, four in numher. Mouth-shields longer 

 than broad, broader ^vithout than within, corners all rounded ; outer 

 side curved, or made up of three lines ; lateral sides re-enteringly 

 curved ; length to breadth, 3.3 : 2.8. Side mouth-shields triangular, 

 small, Inroad, lying entirely on the sides of the mouth-shields. Under 

 arm-plates considerably broader than long ; a little way from the disk, 

 re^^ularly hexagonal ; length to breadth (fourteenth plate), 1.9 : 2.5. 

 Upper arm-plates broader than long, somewhat affected m shape by the 

 number of arm-spines ; most are either hexagonal or oval hexagonal, 

 with very sharp lateral corners; length to breadth (thirteenth plate), 

 1.9 : 4.2. Disk very regularly and finely granulated above, about 14 to 

 a square mm. ; below, interbrachial spaces naked, showing the fine 

 scales. Arm-spines, near base of arm, alternating five and four, rarely 

 six ; farther out, four and three ; at the tip of the arm only three ; 

 upper spine very long, slender, cylindrical, slightly tapering, sometimes 

 a little curved ; other spines smaller ; within the disk the lowest spine 

 is often much flattened and widened at its end ; lengths to that of 

 under ann-plate, 9, 6.8, 5.5, 5.5, 3.5, 3.5 : 1.9. Tentacle-scales two, 

 nearly to the tip of the arm ; outside one oval, inside one more or less 

 irregular. Color, in alcohol, black, the under surface of the arms having 

 a brownish shade. 



VaiHations. — This species presents, with a wide geographical range, 

 a considerable variation in the length of the arms, and in the length 

 and stoutness of the arm-spines. As a rule (not, however, absolute), 

 specunens from the Pacific Islands have longer and more slender arms 

 and arm-spines. It is this variety that I described as 0. tartarea. The 

 original description of Midler is insufficient. 



The specimen above described had spines of the maximum length. 

 Another large specimen, with a disk of 27°"°- and arms of 150'"°'-, had 

 the spines as follows : 6, 5.5, 4, 3.3, 2.7. The spines of another were 

 5.8, 4.5, 3.5, 2.8, 2.5, the disk being 22'°'"-. A partly grown specimen 

 from Kingsmills Islands belonged apparently to this species ; the disk 

 was 20'"'" in diameter, and the spines were 5, 3, 2.6, 2.6, 2.6. A speci- 

 men in the Jardin des Plantes, from the lies Seychelles, had a disk of 

 31'"'"-, and the arm 98'"'" ; the spines being 6, 3.8, 3.8, 3.2. The upper 

 spine was swollen, as in 0. echinata ; the three lower ones flattened, 

 and cut short off at the end. The color was nearly black. I have seen 

 a large specimen from Zanzibar, whose disk had a diameter of 30'"'°", 

 while the longest arm-spine was only 4.6"*"'-. There were only four 

 spines, except, perhaps, at the very base of the arm. 



