160 BULLETIN 82, UNITED STATES NATIONAL MUSEUM 



P 2 is shorter than P! and has somewhat fewer segments; it is also less stiff and 

 markedly more slender. As on the pinnules following the component segments have 

 finely spinous distal ends. 



The succeeding pinnules decrease in length, the shortest being 6 mm. long, and 

 become more slender with longer segments. After the fifteenth brachial the pinnules 

 again increase in length, reaching a maximum of 23 mm. with 22-23 segments which 

 are markedly longer than broad except for the first two, especially the first, which is 

 short, broad, and trapezoidal. 



The disk is 9 mm. in diameter, strongly incised and completely plated. The 

 ambulacral surface of the arms and genital pinnules is prominently plated. Side 

 plates occur on the pinnules. The sacculi are small and little evident, alternating with 

 the side plates. 



The color in alcohol is uniform greenish yellow, for the most part having been 

 extracted by the similarly colored liquid. 



Notes. — Hartlaub said that a small specimen with 11 arms from Albatross station 

 3408 is noteworthy in having the segments of Pi with less smooth distal ends than 

 usual; they are finely spiny as is the case only with the distal segments in the other 

 specimens. From station 3408 there is also a smaller specimen with the arms 45 mm. 

 long, and in addition there are two very small specimens in which the radials are wholly 

 visible and are beset with blunt, short, erect spines. 



Hartlaub said that a noteworthy feature of this new species, in addition to the 

 variation in the number of arms, is the reduction of the interradial contact surfaces 

 of the axillaries and first brachials, and the fact that such contact surfaces may be 

 completely lacking. The IBri are entirely free laterally, being in contact only through 

 the lateral extensions of their broadened proximal ends. Between the contact point 

 of their anterolateral angles and the contact of the lateral angles of the axillaries there 

 is a considerable open space (water pore). Hartlaub pointed out that the same feature 

 seems to occur in Antedon {Thalassometra) multispina, and that Carpenter here re- 

 garded it as a juvenile feature. 



Noteworthy also, according to Hartlaub, is the size of this species which, with an 

 expanse of 350 mm., exceeds almost all the other species in the Basicvrva group. He 

 said it was surpassed by Antedon yPerissometra) flexilis with an expanse of 550 mm., 

 and by A. (P.) robusta with a spread of nearly 500 mm. In giving an expanse of 550 

 mm. (55 cm.) for A. {P.) flexilis Hartlaub was quoting Dr. P. H. Carpenter, but the 

 55 cm. given by Carpenter was an error for 35 cm. 



Hartlaub remarked that in the spinosity of the IBr series and lower brachials 

 there is a decided similarity between this species and Antedon (Thalassometra) bi- 

 spinosa in which, judging from the figures, the elements of the IBr series and lowest 

 brachials are beset with small blunt spines not only along the edges but also over their 

 entire surface. In Th. agassizii this ornamentation runs farther out along the arm 

 and the small quite erect spines are confined to the proximal and distal edges of the 

 ossicles so that eoeh articulation is marked by two transverse rows of spines. 



Regarding the eentrodorsal and the articular faces of the radials (see Part 2, pi. 3, 

 figs. 981-983) Hartlaub said that the cirrus sockets are moderately large and show a 

 conspicuous articular boss. The ventral surface of the eentrodorsal is approximtely 

 pentagonal, with the five angles somewhat prominent. The dorsal surface of the ra- 



