274 VERRILL 



PTERASTER OBSCURUS (Perrier) Doderlein. 



Hexaster obscurus PERKIEK, Mem. Soc. Zool. France, iv, p. 267, 1891 ; Res. 



Camp. Sci., xi, p. 41, pi. in, figs, i, la, 1896. 



Pterastcr (Temnaster) hexactis VERRILL, Proc. Nat. Mus., xvn, p. 275, 1894. 

 Temnaster hexactis VERRILL, Amer. Journ. Sci., XLJX, p. 202, 1895. 

 Hexaster obscurus VERRILL, Revision, Trans. Conn. Acad., x, p. 271, 1899. 

 Pteraster octaster VERRILL, Amer. Journ. Sci., xxvm, p. 61, fig. i, 1909 



(variety). 

 Pteraster obscurus FISHER, op. cit., 1911^, p. 363, pi. cv, figs. 1-4; pi. cvi, 



figs, i, 2. 



The original description of P. hexactis was as follows : 



" Disk broad, very high, evenly convex, with a rather large central 

 opening surrounded by circles of prominent, imbricated, and webbed 

 spines. Rays six, short, broad, tapered to blunt tips, their lateral 

 margins convex. Lesser to greater radii, about as i to 1.5. Lesser 

 radii, 22 mm. ; greater radii, 32 mm. to 35 mm., in the alcoholic 

 specimen ; height of disk, 30 mm. 



" The surface of the disk is covered with very numerous small 

 spinules, covered more or less completely with a thick skin-like 

 membrane, and arranged in irregular, divergent groups. 



" The integument between the spinules is thick, smooth, firm, and 

 everywhere perforated by numerous very small, round pores. 



" In each interradial region there is a narrow, radiating groove, 

 lined with thick naked integument, destitute both of spinules and 

 pores, but showing a wrinkled surface. These grooves commence at 

 about one-fourth the distance from the dorsal center to the margin. 

 In some cases there is only a small slit-like opening in the upper end 

 of the groove, communicating with the space beneath the dorsal 

 membrane, but in some of the interradii the slit is much larger and 

 longer, reaching nearly or quite to the margin, and communicates 

 with a large marsupial pouch, containing well-formed young, some 

 of which were in the act of escaping when preserved. Apparently 

 the slit-like openings are formed, or at least much enlarged, when the 

 young are ready to come forth, and after their birth the edges of the 

 slits may become again united. 



" The dorsal spines or pseudopaxillae beneath the integument are 

 large, stout, rather long, and surmounted with a large divergent 

 group of long, slender spinules. In the interradial region, within 

 the marsupial pouch, there is a group of several lobed or branched 

 papulae at the base of each paxilliform spine. The large spines 

 situated along each side, within these cavities, have rudimentary 

 spinules at the summit, which do not reach the outer membrane, so 



