a new Genus of Oj^Muroidea. 191 



quadrangular or diamond-sliaped ; tliey 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 ar- 

 rangement ; and they are seen, more or less modified, in the 

 fom*th 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 out- 

 line, broader than long; it supports five, short, closet en- 

 tacle-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 ten- 

 tacle-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 is the 

 broadest, is short and 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. 



Between the tentacle-scales of these first five or six tentacles 

 and the generative slit there are occasionally one or two 

 spinules. 



Towards the mid arm, the side arm-plates are tumid at the 

 sides, nearly flat below, broader than long, and shortest where 

 they are joined longitudinally. They have a sharp bend to 

 reach the side of the arm, and terminate above in an angular 

 edge by joining the outer edges of two upper arm-plates. 

 Their distal margin, at the side of the arm, is thick, and sup- 

 ports two very small, distant, irregulai", sharp, short spines 



