472 PEOr. p. M. DUNCAN ON SOME 



of the side arm-plates, close to tlieir outer free edge. The arms 

 taper rather suddenly, and are bent downwards after death, giving 

 a very spidery look to the form. 



The first under arm-plate is small, longer than broad, broadest 

 within, where there is a slight re-entering curve in the midst of a 

 convex inner border, and much narrower distally, where there is 

 a rounded process sej)aratiug the side mouth-shields, and termina- 

 ting close to the junction of the first side arm-plates on the arm. 



The second under arm-plate is much larger than the first ; it is 

 broader than long, projects slightly, and is broadly heart-shaped iu 

 outline. The inner part is angular, and the outer broadly curved, 

 and the angular sides are rounded. The next arm-plate, separated 

 by well-developed side arm-plates, which meet longitudinally 

 along a straight line, is less angular orally ; and the fourth arm- 

 plate, much broader than long and smaller on the whole, has its 

 sides slightly straighter than those already mentioned. The suc- 

 ceeding under arm-plates are smaller, have the sides straighter, 

 and the distal curve is less developed than the oral. At the tip 

 of the arm the lower plates are much smaller and widely separate, 

 their sides are straight for a short distance, the curve is more in- 

 tense without than within, and the whole is still broader than long. 



The upper arm-plates are widely separated, small, slightly 

 broader than long, angular within, faintly re-enteringly curved at 

 the sides and well rounded distally. They are convex above. 

 Near the tip of the arms they are strongly rounded without, and 

 very convex above from side to side and from within externally. 



The side arm-plates are strongly developed, and constricted 

 proximally ; each gradually swells out laterally, broadly, and also 

 superiorly, so as to include the upper arm-plates in a considerable 

 nodosity, which is only lateral inferiorly. They unite above, as 

 below, in straight median lines, and the result is that a side view 

 of an arm presents a tolerably straight condition of the lower sur- 

 face, and a waved edge of alternate depressions and rounded pro- 

 jections of the upper surface. 



The free edge of the side arm-plates, rather stout and pro- 

 jecting at the side of the arm, gives origin to four sharp, glassy 

 spines as well as to a minute spinulose tentacle-scale. The sj)iues 

 are shorter than a joint, are spear-like, striated longitudinally, and 

 are minutely serrate ; the upper are the lai'gest and longest, and 

 sometimes a fifth exists near the disk. The texture of the arm- 



