A MONOGRAPH OF THE EXISTING CRINOIDS 353 



quadrate, becoming blunter and more elongated toward the end of the arm, but without 

 any overlap. 



The first syzygy is between brachials 3+4, the next frequently between brachials 

 11 + 12, though sometimes not until between brachials 19+20, and the distal intersyzy- 

 gial interval is from 2 to 10, generally from 5 to 7, muscular articulations. 



P! is longish with about 30 short segments, of which the proximal are rather flattened 

 on the outer side with a sharp dorsal keel. P a is similar but shorter. P 2 is longer with 

 fewer but larger segments of which the fourth and fifth are broad and expanded toward 

 the ventral side. This expansion increases in the following pinnules, which have the third 

 and fourth segments largest. This is most marked about Pi 2 , but is traceable to the thir- 

 tieth brachial. The remaining pinnules diminish in stoutness without increasing much in 

 length. 



The disk is 7 mm. in diameter, much incised and pretty completely plated as are 

 also the brachial ambulacra. The gonads are protected by stout anambulacral plates. 

 The ambulacra of the distal pinnules have well marked side plates, which are generally 

 notched for the sacculi. The sacculi are large and abundant, especially on the distal 

 pinnules. 



The color in alcohol is brownish white or light yellowish brown. 



Notes. Supplementing the foregoing description Carpenter wrote that this species 

 is readily distinguished from Ch. basicurva by the smoothness of the arms and the ap- 

 pearance of the radials externally. Another point of difference is that the wall-sidedness 

 of the arm bases extends out to the fifth or even the sixth brachial which is not the case 

 in Ch. basicurva. On the other hand, the basal segments of PI and P a in the type from 

 station 170A are less flattened and not so distinctly trihedral as is Ch. basicurva so that 

 the proximal pinnules are more like their successors than is the case in that species. 

 But Carpenter noted that in the two individuals from station 174 (B, C, or D) where 

 Ch. basicurva did not occur the lower segments of PI show a distinct tendency toward 

 the trihedral form characteristic of that type. 



Carpenter said that the radials are completely visible in all the specimens of 

 incisa, though they are shortest in those which are most mature, barely reaching half 

 the length of the IBri, to which they are nearly equal in some of the younger individuals. 

 He remarked that this species has a relatively smaller centrodorsal than basicurva so 

 that the radial pentagon covers it completely, and no part of it is exposed when the 

 IBri are removed. The dorsal aspect of the radial pentagon is much the same in the 

 two types, except for the portion of the radial which appears externally in Ch. incisa. 

 But the lower ends of the muscular fossae in the latter are almost entirely without the 

 ridge and furrow markings which are generally present in Ch. basicurva. The articular 

 facet of the cirrus sockets is relatively smaller in incisa than in basicurca, and the 

 radiating processes around the edge of the socket are less distinct. 



After examining Carpenter's specimens in the British Museum Gislen noted that 

 there are no dorsal spines on the cirri and that the opposing spine is a transverse, not 

 bisected, ridge. On one specimen he found a IIBr 4(3+4) series following which on one 

 arm the first syzygy was between brachials 1 + 2. 



Localities. Challenger station 170A; near the Kermadec Islands, north of New 

 Zealand (lat. 2945' S., long. 17811' W.); 1,152 meters; bottom temperature 4.17 C.: 

 volcanic mud; July 14, 1874 [von Graff, 1884, 1885, 1887; P. H. Carpenter, 1888; 



