150 Bulletin, Vanderoilt Marine Museum, Vol. IV 



the anal system. The actinostome is deeply sunken with the posterior 

 lip very prominent and projecting almost as far as the anterior margin 

 of the actinostome. The anal system is small, elliptical, covered by 

 irregular, polygonal plates supporting spines, diminishing rapidly in 

 size toward the anal opening. The margin of the interambulacra adja- 

 cent to the ambulacral plates of the lower side, the space around the 

 anal system and around the actinostome is closely packed with two 

 kinds of pedicellariae. 



The large, tridentate pedicellariae are rare (fig. C), and have the 

 head about one-fourth longer than that of the large, globiferous pedi- 

 cellariae, slender, tapered, the tips of the valves dentate, meeting. 



The actinal pedicels are stout, very muscular, with the distal end 

 divided into a mat-like mass of numerous, (20 to 30), tiny tentacles. 



The primary spines around the actinostome are somewhat longer 

 than the others, curved basally, verticillate, distally flattened, with a 

 deep groove on the under side. 



The large globiferous pedicellariae are rare and have a very long 

 stem, about four times the length of the head. The head has three 

 valves, forming a slightly convex, three-sided, cup-like base, with the 

 distal three-fifths of each valve slender throughout its length, but 

 narrower proximally than distally, where is has a rounded, dentate 

 margin. 

 References: Spatangus ventricosus Lamarck, Anim. sans Vert., vol. 



3, p. 29, 1816. 

 Meoma ventricosa Lutken, Vid. Meddel. Naturk. For. Kjobenhavn, 

 p. 120, 1863. — A. Agassiz, Mem. Mus. Comp. Zool., vol. Ill, part 

 1, p. 358, pi. XX, fig. 8, pi. XXII, figs. 3, 4, 1872; Kept. "Chal- 

 lenger" Echinoidea, vol. Ill, p. 221, 1881. — H. L. Clark, Rept. 

 U. S. Fish. Comm, vol. XX, part 2, p. 255, 1901 ; Cat. Recent Sea 

 Urchins, Brit. Mus., p. 220, 1925. — Mortensen, Th., Danish In- 

 golf Exped. Echinoidea, vol. IV, part 2, pp. 184, 185, 186, 189, 

 194, 1907. 



HOLOTHURIOIDEA. 



Order: ELASIPODA. 



Family: PELAGOTHURIIDAE. 



Genus : PELAGOTHURIA Ludwig. 

 Pelagothuria natatrix Ludwig. 



Illustration: See Ludwig. 



Type: Ludwig had 18 specimens, taken by the "Albatross" at 

 eleven stations in the vicinity of the Galapagos Islands, Cocos Island 



