136 Bulletin, Vanderbilt Marine Museum, Vol. IV 



are wide, this width increasing underneath; above, the pores are 

 arranged in oblique, slightly curved rows of four or five pairs, but on 

 the lower surface they are more transverse in nearly straight rows 

 of four pairs, with rows of tiny tubercles intervening. There are two 

 rows of primary tubercles on the ambulacra with an irregular, median 

 row of smaller tubercles between them. The interambulacra have two 

 primary rows of somewhat larger tubercles midway between the 

 lateral margin and median line and a row of smaller ones on each 

 side bordering the poriferous zones, also a median double row of 

 alternating tubercles of still smaller size. The genital plates unite so 

 as to separate the small ocular plates from the anal area. The 

 madrepore is small, transversely oval. The majority of the spines 

 are less than half an inch long, moderately slender, tapering, with 

 many fine, longitudinal striations, the ribs crossed by numerous fine 

 lines. 



The figures of the pedicellariae given were of necessity made from 

 dried specimens. The stout, tridentate pedicellariae are rare, six to 

 eight per urchin, and have the stalk slender, about two-thirds as 

 long as the head which is 1.6 mm. long and quite wide at the base, 

 the median part of each valve narrowed, the apical part widened 

 somewhat, the margins regularly toothed, meeting closely on those 

 of the adjacent valves. 



The slender tridentate pedicellariae are fairly abundant on the 

 dorsal surface and have the stalk very slender, four to five times as 

 long as the head which is very small, has the base of each valve broad, 

 the distal three-fifths slender, with the apex slightly wider and 

 toothed. (See figure B.) 



The small globiferous pedicellariae are very abundant on the actinal 

 region, each with a slender stalk approximately the length of the head, 

 the valves as figured, taper to a point and are closely toothed on 

 the margins. 



References: Echinus (Toxopneustes) gibbosus L. Agassiz et E. De- 



Sor, Ann. Sci. Nat., vol. VI, p. 367, 1846. 

 Strongylocentrotus gibbosus A. Agassiz, Mem. Mus. Comp. Zool., 



vol. Ill, part I, p. 164, 1872 (and synonymy). — H. L. Clark, 



Proc. Wash. Acad. Sci., vol. IV, p. 526, 1902 ; Bull. Mus. Comp. 



Zool., vol. 52, p. 346, pi. 12, fig. 2, 1909. 



