50 OPHIOGLYPHA NODOSA. 



and narroAver within. Side arm-plates occuping a large part of the 

 under surface, but not meeting below till about two thirds out on the 

 arm ; swollen, thick, rounded, projecting laterally, so as to make vertical 

 creases along the sides of the arm ; not meeting above till close to the 

 tip. Upper arm-plates small and swollen, much broader without than 

 within, outer side curved, mner side nearly straight, lateral sides straight ; 

 length to breadth (fifth plate), .8:1; the first plate is triangular, and 

 very minute ; this and the second plate are included by the notch in 

 the disk ; at the point of the arm the plates become triangular, with 

 the outer side rounded. The primary plates of the disk are irregular 

 in shape, stout, and swollen, but are regularly arranged ; in the centre 

 of the disk, above, there is a close rosette of six ; one in the middle, 

 having a diameter of 1.4"""', and five more, rather smaller, ranged about 

 it ; there are two more separate ones in each interbrachial space, of 

 which one is just on the margin of the disk ; the spaces between the 

 primary plates are filled with closely crowded smaller scales, of various 

 shapes. Kadial shields longer than broad, broader without than within, 

 irregular in shape, corners rounded ; joined except at their inner ends, 

 where they are separated by a single scale ; length to breadth, 1.5 : 1.1. 

 Along the free edge of the radial scale, and so passing downwards and 

 inwards along the whole length of the genital slits, is a close row of 

 about eighteen short, stout papilla?, which are longer and more pointed 

 above, and gradually become very minute below ; the longest have a 

 length of about .2"'"'. Arm-spines near base of arm, commonly one, 

 sometimes two, very short, blunt, and rounded ; length about .2"""-. 

 The tentacle-scales on the inside of the pores resemble the arm-spines, 

 and near base of arm are four or five in number ; those on the outer 

 side are similar, but are a little broader and flatter ; on the first three 

 or four j^ores there are two, then one, and, nearer the end of the arm, 

 none ; on each side of the innermost tentacle pore are three, sometimes 

 four, scales, in a close row ; they resemble the others, but are rather 

 broader. Color, in alcohol, dull gray. 



Variations. — The proportions of the arms to the disk may be 5 : 9, 

 5:10, 6:10.5, 7:0.5; or, according to Liitken, 6.5:16, or 8.5:17. 

 There maj- be either one, two, or three arm-spines, near the base of the 

 arm. This irregularity might be expected in such ill-developed parts. 



0. nodosa may be told from 0. Stuwitzii by its regularly arranged 

 primary plates, and arm-spines separated from the tentacle-scales ; the 

 arms also are longer. It has been found on the coasts of Greenland 

 and Newfoundland. 



