PROCEEDINGS OF THE NATIONAL. MUSEUM. 



VOL. 64, 



LYSASTROSOMA ANTHOSTICTA Fisher. 



Description. — Rays 5. R=63 mm., r=9 mm., R=7r; breadth of 

 ray at base, 8 to 10 mm. Disk small ; rays marked off from disk by 

 a slight constriction at base. The whole body is very weak and 

 flabby much as if it had been decalcified. This is due to the absence 

 of a connected abactinal skeleton and also to the very loose connec- 

 tion between the marginal plates. Even the ambulacral and adam- 

 bulacral plates are rather loosely articulated and the plates them- 

 selves are not hard and firm, but rather spongy. 



The abactinal skeleton consists of widely separated, entirely dis- 

 connected, small irregular or faintly lobed plates, ordinarily from 

 0.4 to 0.6 mm. in diameter, each bearing a slender acicular spine 

 surrounded by a thick, tough sheath, broadly expanded at the sum- 



FlG. 1. LYSASTROSOMA ANTHOSTICTA X 10. MARGINAL AND 5 ABACTINAL PLATES FROM 



PROXIMAL HALF OF RAY ; BASE OF RAY TO THE RIGHT ; a a a, ABACTINALS ; S S S, SPINIF- 

 ERODS SUPEROMARGINALS ; i i, INFEROMARGINALS ; ad, ADAMBULACRALS ; SECONDARY 

 MARGINALS SHOWN BETWEEN THE SUPEROMARGINALS. 



mit, which is very thickly beset with crossed pedicellariae. These 

 spinelets (1 to 1.5 mm. long) are conspicuously smaller than the 

 superomarginals, and are not at all in regular series. There appears 

 to be the equivalent of about five longiseries, although at the base of 

 some rays the arrangement is far too irregular to admit of exact 

 determination. Scattered all over the abactinal surface, among the 

 spiniferous plates and completely immersed in the integument, are 

 numerous perforated " vestigial " plates of a generally subcircular 

 or elliptic contour, which resemble holothurian plates and are 0.08 to 

 0.18 mm. in diameter. The skin is rather thickly beset with small, 

 lanceolate straight pedicellariae of several sizes, the number varying 

 in different examples. 



Alternate superomarginal plates are spineless and smaller than 

 the spiniferous. While at the very base, of the series they touch one 



