A MONOGRAPH OP THE EXISTING CRINOIDS 557 



broad and the shorter distal segments about half again as long as broad; the 16-26 

 arms are 70-80 mm. long; P, is 6-6.5 mm. long, with 15-18 segments; P, is 7 mm. 

 long, with 22 segments; P 3 is 9 mm. long, with 23 segments; P« is 8 mm. long, with 

 20 segments. Except for the slender, long-jointed cirri this species does not differ 

 in any essential feature from D. flagellata. 



Description. — The centrodorsal is low hemispherical with very sloping sides, the 

 dorsal pole slightly convex, flat or very slightly concave, 1.5 to 2.5 mm. in diameter. 

 The cirrus sockets are arranged in two, or in two and a partial third, irregular and 

 crowded marginal rows. 



The cirri are XIX-XXVIII, 25-28 (usually 26), 20 to 25 mm. long, slender and 

 delicate; the tenth-twelfth (usually the twelfth) is a more or less marked transition 

 segment. The first segment is very short, the second is twice as broad as long, the 

 third is slightly broader than long, the fourth is half again to twice as long as the 

 median width, and the fifth is two to two and one-half times as long as broad. The 

 following to the ninth, tenth, or eleventh are similar, the remainder slightly shorter, 

 about half again as long as broad. The tenth-twelfth and following segments 

 have prominent triangular median spines; after one or two segments these spines 

 occupy about half of the middorsal line, the anterior (distal) margin standing out 

 vertically and one-half to one-third as long as the recumbent side, the hypothenuse, 

 from the apex of the spine to the proximal base, straight, its proximal end sometimes 

 marked by a slight tubercle, or slightly concave, running from the distal spine to a 

 smaller blunt proximal tubercle. The spines change but little distally, their bases 

 becoming slightly shorter and their apices consequently sharper, and the hypothenuse 

 straight. The opposing spine is longer than the spines on the preceding segments and 

 more slender, median or submedian, nearly or quite erect, nearly or quite equal to the 

 width of the penultimate segment in height. The terminal claw is longer than the 

 penultimate segment, very long and slender, slightly and evenly curved. The longer 

 earlier segments have slightly enlarged ends, this feature becoming less marked in the 

 spiniferous distal segments, though traceable quite to the penultimate. 



The division series and arms resemble those of D. flagellata, but are much more 

 slender and delicate. The division series and first brachials may be well separated, 

 or they may be in lateral contact; they are usually not quite in apposition, though they 

 have straight lateral edges which are usually slightly swollen. The characteristic 

 rugose appearance of D. flagellata, due to the low, though prominent, synarthrial and 

 articular tubercles, is reflected in a delicate and modified form. 



The arms are from 16 to 23, from 70 to 80 mm. long. 



Pi is 6.0 to 6.5 mm. long, with 15 to 18 segments, of which the first is short, the 

 second nearly as long as broad, and the seventh or eighth and following slightly longer 

 than broad. P 2 is 7 mm. long, with 22 segments, of which the first is short, the second 

 about as long as broad, the third slightly longer than broad, and the seventh or eighth 

 and following half again as long as broad, becoming twice as long as broad terminally. 

 The pinnule is very slightly stouter basally than P 1; but tapers less rapidly and more 

 gradually, and is less flagellate distally. P 3 is 9 mm. long, with 23 segments, resembling 

 P 2 but proportionately stouter. P 4 is 8 mm. long with 20 segments, resembling P 3 ; 

 the second-fourth segments are sometimes very slightly enlarged. P 5 is 4.5 mm. long, 

 with 14 segments, of the same character as P< but proportionately smaller. P 9 is 



