A MOXOGRAPH OF THE EXISTING CRIXOIDS 



465 



profile of the cirri is smooth in the basal half, and serrate with more or less broad teeth 

 in the distal half. 



The radials are oblong, about twice as broad as long, rather longer in young and 

 shorter in very large individuals. The IBr, are oblong, longer than the radials, with 

 the distal border rather deeply incised and the lateral borders straight and sharply 

 flattened against those of their neighboi-s on either side. The IBrj (axillaries) are 

 about as long as broad with a sharp distal angle. On the articulation between these 

 two ossicles there rises an extravagantly elongated synarthrial tubercle. 



The 10 arms are from 65 to 90 mm. in length. The first two brachials are relatively 

 very large, irregularly quadrate with the shorter side in, the articulation between them 

 rising into an enormously elongated S3'narthrial tubercle similar to that between the 

 elements of the IBr series. The third brachial (the hypozygal of the first syzygial 

 pair) is low triangular with the apex of the triangle on the outer side. The fourth 

 brachial (epizygal) is short and oblong, almost discoidal. The fifth and sixth brachials 

 are oblong, longer than the fourth. The following 4 or 5 brachials are slightly wedge- 

 shaped, those following becoming triangular, about as long as broad, and distally 

 wedge-shaped again and elongate. The earlier brachials, to about the eighth, are in 

 close apposition to those on the adjacent arms against which they are sharply flattened. 

 There is often, in large specimens, a considerable development of articular tubercles. 



Syzygies occur between brachials 3 + 4, 9 + 10, and 14 + 15, and distally at intervals 

 of 4 muscular articidations. The width at the fii'st syzygy in the type is 1.5 mm. and 

 the length from the IBrj to the second syzygy is 11.5 mm. 



P] is 7 to S imn. long, moderately slender and evenly tapering, composed of 14 to 

 15 segments [A. M.C.], of which the first is short and the remainder are about twice 

 as long as broad. Pa is absent. P2 is similar to Pj and of about the same length. 

 P3 is similar, but slightlj- shorter, about 7 mm. long. P< and Pj are shorter still, 4 mm. 

 long and composed of about 10 segments, but resemble the preceding in character. 



oocriz 



mm 



Figure 20.—Perometra diomedtae (A. H. Clark), holotype: a, Pi; b, P,; c, nonperipheral cirrus. 



