80 



varies somewhat, often differing on the different arms of the same 

 individual. A specimen with a disc of 23 millim. had arms of 

 161 millim.; length of arm-spines to under arm-plate, 4.5, 4, 3, 2.5: 

 1.4. A small specimen had the disc 14 millim.; arms, 110; arm- 

 spines to under arm-plate, 4, 2.5, 2, 1.6 : 1.1. 



This is the representative species of 0. scolopendrina, from which, 

 however, it is distinguished by longer arms and longer and more 

 slender arm-spines. The tooth-papillae, also, are usually fewer. 

 Kingsmill Islands. 



Ophiocoma insularia, Lyman. 



Special marks. Lower spines longer than the upper. Arms flat, 

 about four times as long as diameter of disc. Under arm-plates 

 regular, and about as long as broad. Interbrachial spaces below 

 closely granulated. 



Description of a specimen. Diameter of disc 30 millim. Width of 

 arm, without spines, 4.5 millim. Length of arm, 125 millim. Mouth- 

 papillse, six on each side ; under the teeth there cannot be said to be 

 any mouth-papillae, because the tooth-papillae, which sometimes are as 

 many as twenty, extend downwards and outwards, growing smaller 

 and smaller, till they nearly reach the inner end of the mouth-shield. 

 Teeth four, flat and squarish ; upper one smallest. Mouth-shields 

 about as long as broad, much rounded, without straight lines ; length 

 to breadth, 2.8 : 2.5. Side mouth-shields small, triangular, lying 

 entirely on the sides of the mouth-shields. Under arm-plates about 

 as broad as long, bounded without by a curve, and within by a short 

 inner side and two inner laterals ; length to breadth (15th plate), 2.2. 

 Upper arm-plates even and regular, much broader than long, bounded 

 without by a clean curve, and within by an inner side and two inner 

 laterals ; length to breadth, 2 : 4. Granulation of the disc extremely 

 close and fine above and below ; and extending even to the outer 

 corner of the side mouth-shields ; about 45 to a square millim. Arm- 

 spines rather short, little tapering, blunt, a good deal compressed ; on 

 the first few joints, beyond the disc, four, very rarely indeed 'five, 

 further out three ; they do not alternate three and four, as is seen in 

 many other species; lengths, to that of under arm-plate, 3, 3.1, 3.6, 

 3.5 : 2. Tentacle scales, two, large and regular, much longer than 

 broad. Color, in alcohol, above, deep umber, almost black ; below, 

 interbrachial spaces the same ; arms a little lighter. 



Variations. A young specimen, with a disc of 9.5 millim. had arms 

 35 millim. long ; the mouth-shields were narrower than in the adult, 

 the color was paler, and the tips of the arms were cross-barred with 

 white. A very large specimen with a disc 33 millim. in diameter, had 

 arms 155 millim. long; the proportion of the arm-spines to the under 

 arm-plate was 3.5, 3.5, 3.7,3.7:2; the upper spines were greatly 



