ARCTIC SEA TO THE WEST OF GREENLAND. 57 



central angular process on the distal and proximal edges, from which there is a reen- 

 tering curve on either side to the lateral angles of the sides of the plate. 



The third lower arm-plate is very broad, extending across the arm ; it is short, the 

 relation of length to breadth being one to three ; the sides are incurved for the 

 tentacle, and are slightly convex towards their distal angle. There is an angular 

 process or cusp on the broad oral margin, and a smaller one on the aboral ; and there 

 is a reentering curve on both sides of the processes, giving a very elegant outline. 

 The fourth lower arm-plate is as broad as the third ; but it is shorter, and the proximal 

 angular process is more decided than that on the distal edge. The next plate has the 

 general shape, but is shorter, and the proximal angle is more pronounced. From this 

 plate to the end of the arm the others narrow more and more, become angular at the 

 sides and more or less triangular as a whole, and are broader without than within. 

 There is a projection in the median line on the aboral margin, and a reentering curve on 

 either side to the lateral angles ; and the proximal angular process has faintly reentering 

 curves on either side of it. Far out and towards the tip of the arm, the lower plates 

 become more quadrangular or diamond-shaped ; they are small, broader than long ; and 

 there is an angular process without and within. At the tip the minute lower arm-plates 

 have the distal edge curved, and they are angular orally. 



The first lower arm-plate is separated from the side mouth-shields by several scales 

 or plates, which are continuous with the base of the tentacle-scales already mentioned 

 as being within and at the sides of the plate. 



The second lower arm-plate has two or three small tentacle-scales on it. In 

 some arms they are fused into one ; or there may be several minute accessory scales 

 present. 



The third plate has the same number and accessory arrangement ; and they are 

 seen, more or less modified, in the fourth and fifth. The other lower arm-plates have 

 no tentacle-scales. 



The side arm-plates form much of the lower surface of the arms, and also the 

 greater part of the sides in mid arm and towards the tip. All unite with their fellows 

 along the median line below ; and all are convex from side to side. The first, just 

 touching its fellow in the median line, is oval in outline, broader than long; it supports 

 five, short, close tentacle-scales on a curved base ; and the tentacular opening is large 

 and circular, having a rim of membrane. The second is broader than the first, 

 touches its fellow, and has four tentacle-scales, and sometimes a fifth or a small 

 accessory one. 



The third side arm-plate, still broader than long, and not much longer than the 

 second, touches its fellow by a longitudinal short and straight line. The margin without 

 is curved boldly, and within very slightly. Like the others it is flat below ; and it has 

 three tentacle-scales, the outer one being subspiniform. The fourth, still broader, is 

 not longer ; and its outer end is large and supports three tentacle-scales, one of which is 

 sometimes wanting. The fifth plate the broadest, is short, and is narrow towards the 

 median line, where it has two small tentacle-scales close together ; and there is a spinule 

 external to them, and sometimes a second. 



I 



