PART 5 A MONOGRAPH OF THE EXISTING CRINOIDS 557 



with the lateral angles slightly separated by a narrow V-shaped notch. The IBri are 

 short, from 4 to 6 times as broad as long in the median line, with straight and parallel 

 sides and the distal border more or less concave; sometimes the arched dorsal surface 

 decreases in width distally, in which case there is a flangelike ventrolateral produc- 

 tion of the laterodistal angles. The IBr 2 (axillaries) are about as long as broad, or 

 a little broader than long, with slightly truncated lateral angles; the concave distal 

 sides form a right angle with each other while the proximal angle is obtuse and 

 broadly rounded. The sides of the IBr series are straight, and usually in contact 

 throughout their length with those of their neighbors. 



The 10 arms are up to 165 mm. in length, and consist of about 200 brachials. 

 The first brachials are about 3 times as long exteriorly as interiorly, with the inner 

 half of the distal border parallel to the proximal and the outer half curving broadly 

 and extending far distally; the outer edge is straight; the inner edge is straight, entirely 

 free, and making an angle of from 45 to 60 with that of its neighbor. The second 

 brachials are much larger, about as long as broad, with the proximal angle broadly 

 rounded. The first syzygial pair (composed of the third and fourth brachials) is longer 

 interiorly than exteriorly, usuaUy about as broad as long in the median line. The next 

 4 brachials are wedge-shaped, half again as broad as long, and the following become 

 much more obliquely wedge-shaped, about as long as broad, and distally longer again, 

 being terminally almost twice as long as broad with only slightly oblique ends. 



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

 of from 2 to 8, but most commonly 3 or 4, muscular articulations. 



P! is very slender and delicate, 15 or 16 mm. long, with 30 to 35 segments, of which 

 the first 4 or 5 are about as long as broad with their distal angles cut away and the 

 following rapidly become elongated, the tenth being more than twice as long as broad 

 and those in the outer half of the pinnule excessively elongated, though without an 

 appreciable enlargement of the articulations. P 2 is similar and of the same length, 

 but very slightly stouter in the earlier portion. P 3 is much shorter, about as stout 

 basally as P^ but tapering much more rapidly, 5 mm. long, with 12 segments, of which 

 the first is slightly broader than long, the second and third are about as long as broad, 

 the fourth is slightly longer than broad, the sixth is twice as long as broad, and those 

 following rapidly become much elongated. The following pinnules resemble P 3 , and 

 those succeeding slowly increase in length and slenderness. The distal pinnules 

 are exceedingly slender, 12 mm. long with about 20 segments, of which the second is 

 longer than broad and the third and following are greatly elongated, though without 

 noticeably expanded articulations. 



Notes.- Carpenter (1888) wrote that the centrodorsal may be either a thick disk, 

 columnar, hemispherical or conical, but whatever its shape, the functional cirrus 

 sockets are limited to 2 or 3 rows about the equator, all the more apical portions of the 

 centrodorsal having the sockets more or less completely obliterated. 



Baldelli (1914) found from numerous counts that the cirrus segments in the 

 specimens from Washington station III, haul 5, varied from 37 to 50, the average being 

 44. Grieg (1904) in a specimen from La Ciotat found the cirri to be from 51 to 53 mm. 

 long, with 46 to 48 segments. According to Carpenter (1888), the longest cirrus on 

 the Porcupine specimens from Tunis was 52 mm., with 47 segments. 



Baldelli (1914) has paid especial attention to the distribution of the syzygies in 

 this species, his studies having been made on the abundant material secured by the 



