88 NATURAL HISTORY BULLETIN 



shaped, plataleiform, spatulate, or battledore-shaped, rarely pa- 

 pilliform. There may be two to five valves. The valvular form 

 of the pedicellariae first led to the establishment of this group. 



The various kinds of dorsal plates pass into each other by 

 various intermediate forms, so that it is impossible to draw any 

 very strong or sharp family lines on this character alone, though 

 the character of the plating may generally be taken as of generic 

 value. They are more frequently polygonal and tesselated; 

 often in the form of protopaxillae or parapaxillae ; sometimes 

 deeply lobed and openly reticulated ; sometimes imbricated. 



Sometimes they are naked; often spinose; very rarely truly 

 paxillif orm ; sometimes covered by a thick, smooth, or granulated 

 integument. 



Both rows of marginal plates are usually well developed and 

 form a stout margin to the disk and rays. 



Interactinal plates are usually rather numerous and tesselated 

 or imbricated. A distinct dorsal pore is usually present. Gen- 

 ital pores are generally ten, usually all separate, situated in the 

 dorsal interradial areas; sometimes serial on the sides of the 

 rays. 



Superambulacral plates are present in some genera, absent in 

 others. The existence of superambulacral plates, formerly sup- 

 posed to be characteristic of Astropectinidce, occurs in several 

 of the genera now referred to Valvulosa (viz., Mediaster, Di/tas- 

 ter, Pseudar chaster, etc.), and in other groups. 



Adambulacral plates wide, with a longitudinal group of small 

 furrow-spines and with one or several spines on the actinal side, 

 often becoming much longer distally. Jaw-plates are large and 

 usually convex on the actinal surface, bearing numerous oral 

 and epioral spines. 



This is a very extensive group, found in all seas. 



Family Ophidiasteeid^ Verrill. 



OpMdiasteridcB Verrill, Trans. Conn. Acad. Sci., i, part 2, p. 344, 1867; op. 



cit., p. 308, 1914a. 

 LincMadw Perrier, Revision Stellerides, p. 117 [381], 1875. 

 LinchiidcB Sladen (pars), op. cit., 1889, p. 397. Fisher, op. cit., 19116, p. 



240. 



LincTciadcB Yi^iier, Squelette des Stell., p. 144, pi. ix, figs. 1-13; pi. x, figs. 

 1-7, 14-19 (structure), 1879. 



