PROCEEDINGS OF THE NATIONAL MUSEUM. 



VOL. 64, 



rated. The median suture of the first pair of plates is shorter than 

 that of the oral plates (fig. 3). 



Ambulacral furrows wide, with large, very crowded, quadriserial 

 tube-feet. The ampullae are single and very large. The furrow 

 widens at the base, in a very characteristic way, for the length of the 

 first 8 to 12 ambulacral plates. The first two combined ambulacral 

 ossicles are conspicuously enlarged ; the others are very thin, and the 

 pores are in four distinct series. Actinostome large and apparently 



very flexible. The nerve cord of 

 each ray widens abruptly as it 

 approaches the actinostome, and the 

 circumoral cord, or fold, is con- 

 spicuous. 



The madreporic body, sometimes 

 invisible, is situated near the edge 

 of the disk and surrounded by sev- 

 eral spinelets. 



Small crossed pedicellariae (0.2 

 to 0.22 mm. long) are situated, as 

 detailed above, on the distal sur- 

 face of the abactinal and marginal 

 spine sheaths. Their form is best 

 appreciated by the figure (fig. 5). 

 The enlarged tooth, on one side of 

 the jaw, and the numerous shank 

 teeth are characteristic. Straight 

 Fig. 3.— lysastrosoma anthosticta x pedicellariae are small, slender to 

 10. di.u.i:am of plates of mouth ^^-oadly lauceolatc, but delicate and 



ANGLE. l-li, FIRST FOUK SLTKUOMAR- -^ _ ' 



GiNALs; i-iii, FIRST THREE iNFERo- comprcssed ; jaws apparently never 

 MARGINALS ; i, PROBABLE PRIMARY IN- gpatulatc. They arc scattered over 



TERRADIAL PLATE ; m, MOCTH PLATE ; '■ '' 



a, FIRST, ENLARGED ADAMBULACBAL tlic surfacc of tlic body and occur 

 ^^'^™- on the furrow margin and outer 



actinostomial oral spine. Length, 0.15 to 0.65 mm. 



One of the characteristic features of this species is the fact that 

 the rays are slightly spaced on the circumference of the disk so that 

 there is no sharp interbrachial angle. Back of the mouth plates 

 there is a vertical, broad, axillary channel having several fine, 

 probably ciliated, fm-rows leading from the abactinal to the actinal 

 surface. This axillary region is bounded by a distinct constriction, 

 or furrow, which encircles each ray at its base, and beneath the skin 

 a series of small plates extends upward from the interradial mar- 

 ginal plates to the abactinal end of the axillary channel, the last plate 

 being probably the primary interradial (fig. 3, ^). This column 

 acts as a buttress from which a slight but tough membranous inter- 



