79 



with O. erinaceus. I have seen, however, a number of large speci- 

 mens of 0. erinaceus, from Zanzibar, and have compared them with 

 the present species ; and they seem to be distinct, differing as " rep- 

 resentative species " usually do. The upper arm-spines of 0. erina- 

 ceus are more regular, stouter, and more swelled at the base ; also 

 they are shorter ; the upper arm-plates are narrower and more 

 crowded ; and the arms shorter. A specimen with a disc of 30 millim. 

 had four arm-spines, as follows : 4.6, 4, 3.5, 3.5. Sandwich Islands. 



Ophiocoma molaris, Lyman. 



Special marks. Arms five and a half to eight times the diameter of 

 the disc. Spines ringed with darker and lighter ; upper one slender, 

 little tapering, longest, from three to three and a half times as long as 

 an under arm-plate. 



Description of a specimen. Diameter of disc, 24 millim. Width of 

 arm without spines, 4 millim. Length of arm, 137 millim. Mouth- 

 papilla, 11 or 12, the innermost two much the smallest. Tooth- 

 papillae, 7 or 8, rather large. Teeth, four,- upper one narrowest and 

 sharpest. Mouth-shields longer than broad, much narrower within 

 than without, pretty regular; bounded without by a curve, within 

 and on the sides by straight lines ; length to breadth, 2.6 : 2. Side 

 mouth-shields small, triangular, Ipng on the sides of the mouth- 

 shields. Under arm-plates rather broader than long, hexagonal, the 

 outer side and outer laterals being more conspicuous than the cor- 

 responding sides within ; length to breadth (10th plate), 1.5 : 2. 

 Upper arm-plates broader than long, quite irregular, ^.varying in 

 breadth according to the encroachment of the upper arm-spiues, oval, 

 with pointed lateral corners ; length to breadth (7th plate), 1.5 : 3.4. 

 Disc regularly, but rather loosely granulated, 20 to a square millim. ; 

 below, interbrachial spaces granulated, except a band along each 

 genital slit. Arm-spines near base of arm, alternating four and three, 

 slender, elegant, little tapering, somewhat flattened ; upper one longest 

 and largest, but never swelled : lengths to that of under arm-plate, ■ 

 5.5, 3.5, 2.5, 2 : 1.5. Tentacle scales two, on base of arm, but, a little 

 way out, only one. Color, in alcohol ; above, umber brown ; below, 

 interbrachial spaces the same, the other parts lighter ; some of the 

 arm-spines ringed with Ughter. 



Variations. The arms are always slender, long, and finely taper- 

 ing ; but their proportions vary from five and a half to eight times 

 the diameter of the disc. The tooth-papillEe are commonly about 

 nine; rarely 12. The color vaiies in depth; the lightest specimens 

 are pale bluish-gray, varied with specks and marblings of white ; 

 below, nearly white, with brown lines round the under arm-plates. 

 The lighter the color, the more conspicuous are the dark rings round 

 the spines. The number of joints furnished with two tentacle scales 



