84 NATURAL HISTORY BULLETIN. 



sometimes absent. Side arm-plates are united below, and 

 cover most of the under side of the arms. They bear a row 

 of few. small, rough spines or spiniform tentacle-scales, which 

 are usually hook-like distally. Two or more rows of small 

 plates run up from each of the side plates and form trans- 

 verse ridges around the arms, covered with granules; these 

 usually bear rows of small glassy hooks. The dorsal arm- 

 plates are rudimentary or wanting. The entire surface of the 

 arms and disk above and below is covered with cuticle which 

 is usually granulated, so that the plates are hidden. 



ASTROPHYTON MURICATUM (Law.) AgdSsiz. 



Astrophyton costosum Seba, {non Linck), III, pi. IX, fig-. 1, p. 16, 1758 

 (not binomial). 



Euryale muricatum Lamarck. Hist. Anim. s. Vert., II, p. 538, 1816. 



Astrophyton muricatum. L. Agassiz, Mem. Sci. Nat. Neuchatel, I, p. 

 12, 1835. Mull. & Trosch., Syst. Ast., p. 122. Lutken, Add. ad Hist. 

 Oph., Pt. It, p. 156. Verrill, Notes on Radiata, Trans. Conn. Acad., 

 I. p. 341, 1868. 



Astrophyton costosum L3 r man, Proc. Boston Soc. Nat. Hist., XIX, pi. 

 4; Illus. Catal. Mus. Comp. Zool., I, p. 192, 1865; Lyman, Report Voy. 

 Challenger, Zool., Ophiuroidea, V, p. 257, pi. XXXV, figs. 17-25, 

 1882. Nutting, Narrative Bahama Exp., p. 172. 



The color is light chocolate brown, with irregular blotches 

 of darker brown on the disk. The stout stumps on the radial 

 ribs are variable. In some cases they are crowded, short, 

 blunt, wart-like, and do not extend on the arms. In one ex- 

 ample, from the Bahama Banks, each radial rib bears five or 

 six, mostly in one row, and they are sharp and conical, while 

 ten or twelve smaller conical spines extend along the proximal 

 part of each arm. 



A young specimen (disk 8 mm. in diameter) has but one 

 or two stout spines on each rib; these are blunt, and in some 

 cases two unequal spines are joined at base, as if the smaller 

 were budding from the base of the larger; the spines are 

 white and conspicuous against the chocolate ground-coior. 

 From four to eight smaller, blunt, white, dorsal spines occur 

 irregularly on each arm. The outer ones, situated between 



