SHALLOW-WATER STARFISHES 267 



retroambulacrals, or outer adambulacrals, for they are attached to 

 the outer end of the adambulacrals. They are sometimes short and 

 do not reach the margin, except distally, on the rays; but in 

 Pteraster and some other genera their tips usually reach the margin 

 of the disk. Between the bases of these there is usually a small 

 slit or pore (actinal spiracle or " segmental aperture"), furnished 

 with a calcareous valve. 



Interactinal plates are lacking. Pedicellariae have not been found. 

 Jaws have a series of adoral spines, usually webbed. Epioral spines 

 of large size, in one to three pairs, often without webs, stand per- 

 pendicularly to the jaw ; those of one pair are sometimes specialized 

 and partially hyaline. Ambulacral feet are large, in two to four rows, 

 with large apical suckers. 



The supradorsal membrane may be thin and translucent, with 

 thin muscular fibers, or thick and muscular; it may contain calca- 

 reous spicules, muscular and cartilaginous fibers in the form of a net- 

 work, and often abundant mucous glands. The copious mucus is 

 phosphorescent in some cases (Diplopteraster) . 



The intestine and anal pore are well developed. Sexes are alike 

 externally. 



Subfamily HYMENASTERIN& Verrill, nov. 



The genera Hymenaster and Cryptaster, and their allies, should 

 form a distinct subfamily Hymenasterinae, differing from Pteraster- 

 inae in lacking webbed combs of adambulacral spines and in other 

 characters. It is a characteristic deep-sea group. 



Pythonaster Sladen does not belong to this family. It has no 

 supradorsal membrane, actinomarginal spines, nor actinal spiracles. 



Subfamily PTERASTERIN1E. 

 Genus Pteraster Miiller and Troschel. 



Pteraster MULLER and TROSCHEL, Syst. Aster., p. 128, 1842. Sladen, op. 



cit., p. 470, 1889. Fisher, op. cit., 191 ib, p. 344; analytical table of all 



known species, pp. 368-370. 

 Hexaster PERKIER, Comptes rendus, cxu, p. 1227, 1891 (type, H. obscurus 



Perrier). 

 Tcmnaster VERRILL, Proc. U. S. Nat. Mus., xvn, p. 275, 1804 (type, T. hexactis 



Verrill = H. obscurus Perrier). 



Disk large ; rays five to eight ; ambulacra! grooves turn up distally, 

 more or less, reaching to the upper side of the rays. 



Adambulacral spines form equal, webbed combs; retroambulacral 

 or actinomarginal spines closely appressed, ending in a fringe or 



