PART 5 A MONOGRAPH OF THE EXISTING CRIXOIDS 353 



to 20 mm. This corresponds to an arm length of 150 to 200 mm. When the length 

 to the second syzygy is about 15 mm., the width at the first syzygy is 2.8 to 3.0 mm. 



In young individuals the borders of the elements of the IBr series and of the first 

 two brachials are conspicuously spinous, and these ossicles also bear a low rounded 

 spinous median carination. But after an arm length of usually from SO to 100 mm. 

 has been reached, these characters disappear and the borders and the dorsal surface 

 of these segments, like those of all the succeeding brachials, become quite smooth. 



P! is from 30 to 34 mm. long, and is composed of 75 to 82 short segments, of which 

 the proximal eight to ten are much broader than long and more or less carinate on the 

 distal side, and the remainder are usually about as long as broad. In the short proximal 

 segments the distal and proximal borders of adjacent segments diverge from the median 

 point of contact at an acute angle on either side so that the corners of the segments 

 appear to be cut away, this feature becoming less conspicuous on the shorter distal 

 segments. In the small terminal segments of the outer third of the pinnule the distal 

 border of the segments is more or less produced into a rounded or blunted point so that 

 the distal dorsal profile is more or less sharply serrate. The pinnule as a whole tapers 

 rather rapidly, though evenly, in the proximal half, and becomes very delicate and 

 flexible in the terminal third. P 2 closely resembles P,. It is from 30 to 40 mm. in length, 

 usually slightly longer than P 1( though commonly of the same length, and is composed 

 of a slightly lesser number of segments. The carination of the proximal segments, the 

 cutting away of their angles, and the serrate distal profile in the outer portion of the 

 pinnule are usually very slightly less marked than in P!; but examples of either of these 

 are not definitely recognizable. P 3 is from 28 to 40 mm. long, but usually shorter than 

 P! and P 2 , composed of about 50 segments which are relatively longer than those of the 

 preceding pinnules with their characteristic features much less marked. P 4 and P 5 are 

 about as long as P 3 , or very slightly shorter, reaching as a maximum from 30 to 35 mm. 

 in length, composed of the same number of segments which are, however, of a more 

 generalized type. P 6 is much shorter, about 16 mm. in length, composed of much fewer, 

 about 28, segments, and P 7 is 12 mm. long with the same number of segments. From 

 this point onward the pinnules slowly increase in length so that the distal pinnules are 

 30 mm. long and composed of about 40 segments of which the first is short and more or 

 less cresccntic, the second much longer and trapezoidal, diminishing in width distally, 

 and the following are slender, mostly about twice as long as broad, becoming somewhat 

 longer in the terminal third, but shorter again at the tip. The last six or seven segments 

 bear on their dorsal side numerous spines, sometimes more or less hooklike, and the 

 terminal has two or three groups of large hooks. 



The very considerable variation in the development of the pcrisomic plating along 

 the sides of the ambulacra! grooves has already been described (Part 2, p. 268). 



In some specimens the first two segments of the middle and distal pinnules bear 

 carinate processes, causing them to appear abruptly larger than those succeeding. 



In young individuals, with an arm length up to about 80 mm. or even 100 mm., 

 the lower segments of the proximal pinnules are very finely, but conspicuously, spinous. 



It is seldom that examples of this species are found 30 large and so well-developed 

 as those just described, which are typical of the species in its most perfected form. 



Color (in alcohol). Dark brown, brick red, or light reddish or yellowish brown to 

 gray or white, sometimes washed with violet in examples from Labrador. Small speci- 



