PENTAGONASTER LUNATUS. 25 



character and limits of this genus. Two species were originally referred to 

 Pentagonaster by its founder. The type of one of these is now lost, and its identi- 

 fication rests only on surmise. The second species, however, Pentagonaster semi- 

 hcnafiis, is a well-known and widely distributed recent form, about which there is 

 no doubt. I therefore consider that this form has evei'y claim to be regarded as 

 the type of the genus. The existing species of Pentagonaster are found in the 

 Atlantic, the Pacific, the Indian and the Southern Oceans, and in the Eastern 

 Archipelago ; and the bathymetrical range of the genus extends from 20 to 1500 

 fathoms or more. 



1. Pentagonaster lunatus, Woodioard, sp. PI. IV, figs. 1 a — 1 c. 



AsTERiAS LUNATUS, Woodward, 1833. An Outline of the Geology of Norfolk, 



p. 52, pi. V, fig. 1. 

 TosiA tuNATA, Morris, 1843. Catalogue of British Fossils, p. GO. 



— — Bronn, 1848. Index Palaeontologicus, Nomenclator, p. 1274. 



Body of medium size. General form depressed. Abactinal and actinal areas 

 flat. Marginal contour stellato-pentagonal, the major radius measuring nearly 

 twice the minor radius. Rays short and moderately produced, rather narrow at 

 the base and tapering to the extremity. Interbrachial arcs deeply indented and 

 well rounded. 



The infero-marginal plates are twelve (or more) in number, counting from the 

 median interradial lino to the extremity. They form a broad border to the actinal 

 area of the disk, the breadth of which diminishes rather rapidly plate by plate as 

 they recede from the median interradial line. The largest infero-marginal plates 

 adjacent to the median interradial line measure about 5" 25 mm. in breadth and about 

 3 mm. or a little more in length. The length and breadth decrease as each plate 

 proceeds outward until about midway on the ray, where these dimensions are 

 subequal. On the outer part of the ray the length is greater than the breadth. 

 The infero-marginal plates are distinctly convex on their actinal surface in the 

 direction of the median line of breadth, and are slightly tumid at the margin. 

 Their surface is covered with small, uniform, closely placed, and deeply sunken 

 moniliform punctations, upon which small granules were previously borne, probably 

 uniform in size and closely placed (see PI. IV, fig. 1 c). I am not aware that 

 traces of any pedicellarias have been detected on these plates. 



The adambulacral plates are small and oblong, and bear on their surface ridges 



4 



