BRITISH FOSSILS. 



Decade V. Plate IX. 



HEMIASTER MURCHISON 153. 



[Genus HEMIASTER. Desok, IS-iO. (Sub-kingdom Eadiata. Class Echinoder- 

 mata. Order Echinidas. Family SpatangacesB.) Body obtusely cordate, tumid ; dorsal 

 ambulacra dissimilar, petaloid, lodged in depressions, and surrounded by a simple peri- 

 petai fasciole ; tubercles of the dorsal surface small and similar ; anus terminal, supra- 

 marginal ; no sub -anal fasciole ; mouth eccentric, bilabiate.] 



Diagnosis. H. corpore tumido, amhitu subcordato ; amhulacris dorsal- 

 ibus profundis, postero-laterallhus brevissimis ; fasciola lata, evanescente, 



Synonysis. Spatangus^ Smith, Strat. Sjst., p. 37. fig. 3., ' Brickearth ' 

 plate. Hemiaster incBqualis, Forbes, MS. in Morris's Cat. 2nd edit. p. 81. 

 (not Brissus incBrjualis, Forbes, Pondiclieriy Fossils, 1846, Trans. Geol, 

 Soc. t. 7. p. 160. pi. 19. fc 6.) Hemiaster incequalis, Ag. and Desor, Cat. 

 1847, p. 2. D'Orb. Prod. iv. p. 329.) Micr aster Murchisoni, Morris, Cat., 

 1 st edit. 1 843, p. 55. Bronn, Index, p. 724. Spatangus Wlurchisonianus, Max- 

 tell, 1835, Geol. Tr. 2nd ser. v. 3. p. 210, in part. Desmoulins, Ecli., 

 p. 412. {\\oiEckinospatarigiis3Itirchisoni(E, Konig, Icones, 169. unpublislied). 



A memorandum in tlie handwriting of Professor Forbes suggests 

 that this species might possibly be included in the group of 

 Cretaceous nrchins figured (but not yet described) by M. d'Orbigny, 

 under the name Epiaster, and distinguished by the absence of any 

 fasciole. The species of Epiaster, however, are rather to be regarded 

 as Micrasters wanting the sub -anal fasciole, and in this group should 

 be included the Micraster cov-anguinum, var. gihhus, of Decade 

 III. pi. 10, f. 11, 12. 



The specific name is applied in the belief that this is identical 

 with the Spatangus MurcJiisonioi of collectors, found in the upper 

 Green Sand of Nnrstead a,nd Devizes, although not the species 

 figm-ed. by Konig, Avhich is nothing more than a crushed specimen 

 of Holaster Icevis. 



Description. — The typical specimen (a) is extremely tumid, much 

 more so than is represented (f. 3 and 4) in the plate. The measure- 

 ments and number of ambulacral pores are accurately stated in the 

 following memorandum by Professor Forbes : — 



[v. ix.] 5 I 



