CLARK: NEW GENERA OF ECHINODERMS 121 



Glabraster, new genus 

 Genotype. — Porania magellanica Studer, 1876. 

 This new genus is referable to the family Echinasteridae. The 

 whole animal in enclosed in a thick skin which entirely conceals the 

 plates and all but the tips of the spines; this investment carries minute 

 scattered spicules. 



The ampullae are single. 



The gonads are attached to the dorsal wall on either side of the inter- 

 brachial septum. 



The interbrachial septum is complete and rather large, though 

 entirely membranous; it is crossed in the middle, in a line more or less 

 parallel to its curved inner border, by a narrow band of elongate cal- 

 careous ossicles placed end to end and not always touching, which 

 actinally curves inward and runs adorally to the mouth plates. This 

 band is more or less interrupted and may be present only in part. 



The first ambulacral ossicle is much larger than those succeeding 

 and is widely forked in its proximal half. 



The abactinal skeleton is very wide-meshed, reticulate, formed of 

 very narrow elongate overlapping plates with usually pentalobate 

 spiniferous plates at the more important nodes. 



There is a central pentalobate plate, the lobes being radial in posi- 

 tion, which bears a prominent conical spine; in each interradius 

 about one third of the distance between the central plate and the 

 marginals there is a similar spiniferous pentalobate plate; these five 

 spiniferous pentalobate plates about the central abactinal plate are 

 connected by narrow lines of plates, and from the middle of each of 

 these lines a similar line (radial in position) runs to the central plate; 

 also from each of these five interradial lobate plates lines of plates run 

 out on either side parallel to the interbrachial margin, those from 

 adjacent plates uniting at an obtuse angle in the mid-radial line, so 

 that five triangles which are about twice as wide as high are formed, of 

 which the lines directly connecting the interradial pentalobate plates 

 are the bases. From the apex of each of these triangles, which is marked, 

 by a pentalobate plate bearing a small spine, a more or less irregular 

 series of from four to seven similar spiniferous lobate plates runs down 

 the mid-dorsal line of each arm; these plates are connected in the mid- 

 dorsal line by low elongate plates. From the large spiniferous lobate 

 plates in each interradius a double series consisting of five pairs of 

 elongate plates runs to the marginals; the second pair beyond the 

 lobate plate consists of plates with the adcentral ends broadened, and 

 from these there runs to the proximal mid-radial lobate plate at the 

 arm base a series of narrow plates; from a point midway on this series 

 to the arm tips there is a very irregular interrupted series of similar 

 but smaller plates, from which lines of plates run to each superomarginal 

 and to each node in the mid-radial line. 



Within the wide meshes between the very narrow lines of plates 

 are large papular areas, the integument of which is abundantly dotted 

 with calcareous granules. 



