SHALLOW-WATER STARFISHES 305 



Subfamily ASTEROPIN& Verrill, nov. 



Margins not thin ; upper and lower marginal plates well developed, 

 subequal. Dorsal skeleton well developed, the plates tesselated or 

 stellate-reticulate, with or without spinules or spines. Superomar- 

 ginal plates sometimes with stout spines. Interradial plates numer- 

 ous, in chevrons. Adambulacral spines few. Pedicellarise, when 

 present, bivalve or multivalve. 



The Poraniinae differ in having the marginal plates feebly devel- 

 oped, more unequal, the edges of the disk being thin in most cases, 

 and formed by the inferomarginals ; the dorsal plates are irregular, 

 often partly or nearly all abortive, not forming a regular median 

 row, and usually concealed by a thick, smooth, or else finely spinu- 

 lose dermis ; interactinal plates fewer, in oblique rows, or nearly 

 abortive, or in detached, transverse rows (Tylaster), with or without 

 spinules. Pedicellariae generally lacking. 



Genus Dermasterias Perrier. 



Dermasterias PERKIER, Revision Stell., Arch, de Zool. Exper., v, p. 98, 1876. 



Viguier, op. cit., vn, p. 218, 1878. Sladen, Voy. Chall., Zool., xxx, pp. 



355, 375, 1889. Fisher, op. cit., ignb, 248. 

 Asteropsis (pars) GRUBE, Wieg. Arch., xxm, 1857. A. Agassiz, North Amer. 



Starfishes, Mem. Mus. Comp. Zool., v, p. 106, pi. xv (structure). 



Some of the characters of this genus have not been correctly 

 stated by several previous writers. 



It has more or less numerous small pedicellariae scattered irregu- 

 larly over the dorsal surface. 1 These are partly bivalve and partly 

 trivalve, while four-valved ones often occur. The valves are small, 

 thick, obtuse or rounded. Five-valved ones are rarely seen ; three- 

 valved ones are often the most numerous. Other pedicellariae, of 

 much larger size, often occur just outside of the bases of the inner 

 adambulacral spines. They may stand in a single row, or they may 

 be crowded into two or three rows. (PI. vi, figs. 4, 5.) They are 

 mostly bivalvular, with wide, short, truncate jaws, but some of them 

 have three jaws (pi. vi, fig. 5, P' P') ; occasionally one occurs with 

 four smaller jaws. 



On one of the young specimens, they nearly cover the surface, 

 and most of them have four valves ; some have three, and a few 

 five valves. (See pi. L, figs. i-i&.) 



1 Perrier (Revis. Stell., p. 98, 1876) gives the absence of pedicellariae as a 

 character of the genus. On some specimens from Puget Sound they are very 

 numerous on the dorsal side (var. valvulifera Verrill). 

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