A MONOGRAPH OF THE EXISTING CRINOIDS 503 



3+4) and the next four brachials are transversely oblong with traces of forward and 

 backward projections alternating on opposite sides. The following brachials are 

 longer, though still short and sharply wedge-shaped, considerably broader than long, 

 becoming blunter toward the middle of the arms and squarer toward the ends. The 

 first syzygy is between brachials 3+4, the second is from between brachials 10 + 11 

 to between brachials 21+22, usually about brachials 17 + 18, and the distal inter- 

 syzygial interval is 7 to 13, usually 9 or 10, muscular articulations. The pinnules of 

 the first pair (P l and P a ) are short, slender, and tolerably equal, with about 20 longish 

 segments. The pinnules of the next pair (P 2 and P b ) are twice their length (13 mm.), 

 much stouter, and rather stiff. P 3 is somewhat smaller than P,, and the next four 

 pinnules continue to decrease. The remaining pinnules gradually increase in length, 

 becoming slender and delicate in the outer parts of the arms, but not longer than the 

 pinnules of the second pair. The disk is 20 mm. in diameter, naked, and somewhat 

 incised. The brachial ambulacra are close down between the muscles; those of the 

 pinnules are more fleshy, with closely set sacculi. In color the dorsal skeleton is an 

 alternation of purplish red and white, with alternating double rows of dark spots on 

 the white parts. The disk is dark gray. 



Carpenter said that this species comes very near Antedon laevicirra of the Leyden 

 Museum. It differs, however, in having more numerous cirri, the second radials 

 (IBr : ) less closely united, and shorter axillaries (IBr 2 ). The lower and middle brachials 

 are relatively shorter, and the two pinnules of the second pair (P 2 and P b ) are more 

 nearly equal than in A. laevicirra. The terminal pinnules also are much more delicate 

 and less clothed with perisome. He remarked that the coloring is not unlike that of 

 Antedon (Dichrometra) bimaculata, also in the Leyden collection; but in this species 

 P 3 is larger than P 2 , while the reverse is the case in A. aeguipinna. In the key to the 

 species of the Palmata group in the Challenger report aeguipinna was grouped with 

 laevicirra and imparipinna under the heading "the lower pinnules fairly uniform in 

 size on all the arms." It was said to have P 2 and P& large and tolerably equal, whereas 

 hi laevicirra and imparipinna P 2 is larger than P b . 



Hartlaub regarded aeguipinna as identical with imparipinna. He said that apart 

 from the characteristic coloration of its arms it shows the closest agreement with the 

 specimens of imparipinna that he described from Amboina. The essential character- 

 istic of imparipinna, the strikingly large size of P 2 on the outermost arms, is well 

 marked, although Carpenter did not mention it. P 3 is relatively very small, although 

 the difference between P 2 and P 3 is not so considerable as it might be. Hartlaub said 

 that the specimens from Amboina show that t'lis feature, which as a rule is extraor- 

 dinarily pronounced, is occasionally almost lacking so that the unusual smallness 

 of P 3 cannot be considered as a constant character. 



Hartlaub said Carpenter's statement in the key to the species in the Hamburg 

 Museum that in aeguipinna "the fourth and fifth brachials bear large tolerably equal 

 pinnules" is not, strictly speaking, correct. Hartlaub found in the type specimen of 

 aeguipinna the pinnule of the fifth brachial (P b ) is markedly smaller than that of the 

 fourth (P 2 ). It is true that in the type specimen of imparipinna this difference is 

 much more considerable, but in this specimen P t is of quite unusual size. Hartlaub 

 said that as a very constant character for imparipinna the smallness of the opposing 

 spine, which was also given by Carpenter, may be mentioned. Just how the type 



