ARTHRASTER DIXONI. 91 



FAMILY UNCERTAIN. 

 Genus ARTHRASTER, Forbes, 1848. 



Arms stout and long. Radialia, marginalia, and ventro-lateralia form an alter- 

 nating series of seven very completely articulating similar ossicles, which fit so 

 closely as to leave no conspicuous interstices. Each ossicle consists of an oblong 

 and flattened base with a surmounting ridge. Ventro-lateral plates on actinal 

 surface of disc small and mammiform. Ossicles on abactinal surface of disc 

 hemispheroid with a crenulated edge. All the ossicles possess, as ornament, 

 hemispherical granular prominences. 



1. ARTHRASTER DIXONI, Forbes. PI. XVIII, figs. 1 and la; PL XXIX, figs. 11 



and 11 a. 



AETHEASTEE DIXONI, Forbes, 1848. Mem. Geol. Surv. Gt. Brit., vol. ii, p. 467. 



Forbes, 1850. In Dixon's Geology of Sussex, p. 336, 



pi. xxiii, fig. 1. 

 Dujardin et Hupc, 1862. Hist. Nat. Zooph. Echin. (Suites a 



Buffon), p. 437. 



Forbes, 1878. In Dixon's Geology of Sussex (new ed., Jones), 

 pp. 369 and 370, pi. xxiii, fig. 1. 



Specific Characters. Dorsal ridge of all of the arm ossicles well rounded. 

 No spines present except on the adambulacral plates. 



Material. The best example of this very peculiar starfish is preserved in the 

 British Museum of Natural History, Dixon Coll., 47000. The specimen consists 

 of the remains of four arms, only one of which is at all well preserved. 

 It is the type described by Forbes, and is figured in this Monograph on 

 PI. XVIII. A well-preserved fragment of an arm is also in the possession of 

 Dr. Rowe, of Margate. I have referred two fragmentary specimens presented to 

 the British Museum (E 5023 and E 5024) by Mr. W. McPherson, F.Gr.S., to this 

 species (vide infra). 



Description. A section of the arm is similar at all points. It shows seven 

 ossicles, namely, a radial, the pairs of supero- and infero-marginalia, and a pair of 

 ventro-lateralia. These ossicles all alternate in series, and they closely fit the 

 corresponding neighbouring plates in their respective series. The 'edges of the 

 plates possess articulations which assist in forming this close union. All the plates 



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