ARTHRASTER DIXONI. 91 



FAMILY UNCERTAIN. 

 ^^„„s_ARTHR ASTER, Forbes, 1848. 



Arms stout ami long. Radialia, marginalia, and vcnti'o-latrralia form an alter- 

 nating series of seven very completely articulating similar ossicles, wliirli tit so 

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

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

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

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

 hemispherical granular prominences. 



1. AuTHRASTER DixoNi, Forles. PI. XVIII, figs. 1 and la; V\. XXIX, figs. 11 



and 11 a. 



Arthraster Dixoni, Forbes, 1848. Mem. Geol. Surv. Gt. Brit., vol. ii, p. 467. 



— — Forbes, 1850. lu Dixou's Geology of Sussex, p. 336, 



pi. xxiii, fig. 1. 



— — Diijardin el Huj)'', 1862. Hist. Nat. Zooph. ficliin. (Suites a 



Buffon), p. 437. 



— — Forbes, 1878. lu Dixou's Geology of Sussex (new od., 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 ])rcserved. 

 It is the type described Ijy Forbes, and is figured in tiiis 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.G.S., to this 

 species {vide infra). 



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

 ossicles, namely, a radial, the pairs of supero- and infero-raarginalia, 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 as.si^t in forming this close union. All the ])latcs 



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