OPHIUROIDEA OF THE BAHAMA EXPEDITION. 83 



This curious species is found throughout the West Indies, 

 in 50 to 163 fathoms. Off Cape Hatteras, 48 to 68 fathoms, 

 on Titanidcmn subcrosum, etc., U. S. Fish Comm. Off Barba- 

 dos, on Gorgonclla, Yale Museum. 



This species clings to several species of gorgonians, which 

 it closely imitates by its colors and by the form and orna- 

 mentation of the arms and disk. 



ASTROCNIDA ISIDIS Lyill. 



Trichaster isidis Duchassaing, Animaux Radiaires des Antilles, 1850. 



Astrocnida isidis Lyman, Ann. Sci. Nat., p. I, 1872; Lyman, Report 

 Voy. Challenger, Zool., Ophiuroidea, V, p. 270, pi. XLVI, fig. 2, 

 1882, anatomy; Bull. Mus. Comp. Zool., X, p. 279, 1883; Three Cruis- 

 es of the Blake, vol. II, p. 115, fig. 400, 1888. 



Two young specimens are in the collection, labeled as from 

 Station 69, off Cat Island, in 3 to 13 fathoms. But it is prob- 

 able that this is an error, for it is known only^from rather 

 deep water (56 to 120 fathoms, Blake Exped). 



This species clings to several species of Gorgonella and 

 other gorgonian corals, which it closely imitates in color. 

 Its arms also resemble the branches in form and roughnesses. 



Off Barbados, on Gorgonclla, Yale Museum. 

 Family, GORGONOCEPHALID.-E Ljung. (restr). 



Gorgonoccphalincr (pars) Ljung., 1867. Bell, 1892. 



Arms divided dicbotomously into numerous branches. Disk 

 swollen, with ten prominent radial ribs, covered with cuticle, 

 which may bear granules or scattered spinules, or it may be 

 more or less naked. Radial shields, each composed of sev- 

 eral united plates. Teeth and tooth-papillae numerous, spini- 

 form. Mouth-papillae when present, small, conical or papilli- 

 form. Adoral shields well-developed, but usually concealed 

 by cuticle, sometimes broken into several plates. Oral shields 

 rudimentary or wanting. Sometimes there are five small, 

 madreporic plates, but usually only one. Under arm-plates 

 mostly rudimentary, consisting of two or more small pieces, 



