ARCTIC SEA TO THE WEST OF GREENLAND. 63 



the rhombic scales and the others around them, which are not very definite in shape, 

 have their ornamentation radiating from their own centres. 



In another specimen the scaling is perfectly irregular, no sign of a rosette appears, 

 and the large radial shields are separated by several small scales in some radii and not 

 at all in others, when one large overlapping scale is placed between, or rather overlaps 

 their oral and diverging median line. In other specimens where there is a rosette the 

 oral separation of the radial shields is by three large plates, one being flanked by others, 

 or by two plates, one large and one small, the latter being aboral to the other. The 

 ornamentation is not so much by grains as by cells which are not yet opaque with 

 carbonate of lime. The radial shields are convex, large, and are broadly convex where 

 more or less free aborally ; they are separated aborally by small upper arm-plates, in 

 some instances two, and in others three in number. The shields, thus separated aborally, 

 and, as has been mentioned, orally, are united in some instances along a very short 

 line. With regard to the upper arm-plates within the notch, the first is often more 

 or less triangular in shape, with rounded edges, and the apex is oral ; and when this 

 shape prevails, this plate is usually larger than the second, which is broad, short, and 

 sometimes notched distally. The third is larger, and shaped more or less like the 

 second. 



The spinules, which are stout, distinct, and more or less grouped in two rows, are 

 not often more than six or eight in number. They are beyond the radial shields, and 

 appear to be on the derm between them and the upper arm-plates. It is evident that 

 in some specimens there is a spine, or even two (but not in all radii of one specimen), 

 on either side of the first and second arm-plates, and even on the third. This distribu- 

 tion of a few well-developed, short, stout, blunt spines is very characteristic. In some 

 specimens, and in the largest, the first upper arm-plate is in two pieces. 



The coloration of the upper part of the disk varies from a perfect white to a 

 spotted state, with indefinite blue, black, and white, and brown and white. Blotches 

 appear on the centres of the radial shields and larger plates, so that the whole assumes 

 a maculated appearance. The slate-blue colour, very light iu its intensity, may prevail 

 so much on the disk that the white parts come out very decidedly ; and usually that is 

 the colour of the third row of the rosette, of the scales external to the radial shields, 

 and of some scales in the interbrachial spaces near the edge. 



The upper arm is banded in some specimens with the disk-colour and white ; and 

 usually the colour is lost towards the termination of the arms. 



The upper arm-plates are much more convex in their distal curve in some specimens 

 than in others ; but in all they are much broader than long near the disk, and in 

 mid-arm take on the kite-shape with the angle oral and the convex curve distal. 

 Gradually they become longer than broad ; and towards the end of the arms the side 

 arm-plates meet above. 



There is some variation in the shape and size of the mouth-shields ; but their acute 

 oral angle and broad aboral part are invariable. The side mouth-shields are small, 

 narrow, much curved, and just reach to the end of the generative slit. Owing to the 

 angular nature of the proximal part of the mouth-shields, the side mouth-shields, with 



