FROM THE UPPER GREENSAND. 281 



It was afterwards figured and described by Agassiz as Holaster complanatus, and 

 subsequently separated from that group to form the type of his genus Toxaster. As this 

 corresponds with the Echinospatagus of Breynius, the laws of priority demand the 

 restitution of the original name, however much we may regret these changes of 

 nomenclature. 



Echinospatagus Murchisonianus, Mantett, 1835. PI. LX, figs. 1, a — i, and 



PI. LXIV, fig. 1. 



Spatangus Murchisonianus, Mantel. Geol. Trans., 2 ser., vol. iii, p. 210, 1835. 



— — Besmoulins. Tableau des Echinides, p. 412, 1837. 

 Micraster Murchisont, Morris. Catalogue of Brit. Fossils, p. 55, 1843. 



— — Bronn. Index Palseontologicus, p. 724, 1848. 

 Hemiaster in,equalis, Forbes. Morris's Catalogue of Brit. Foss., 2 ed., p. 81,. 



1854. 



— MuRcmsoNiiE. Forbes. Mem. of Geol. Surv., decade v, pi. ix, 1856. 



— — Desor. Synopsis des Echinides Foss., p. 369, 1857. 



— Murchisonianus, Be Loriol. Echin. Helv. Cretaces, t. ii, p. 374, pi. xxxii, 



figs. 4—6, 1873. 



Diagnosis. — Test cordiform, often much inflated, length and breadth nearly equal ; 

 round, and largely grooved before, contracted behind, and obliquely truncated on the 

 posterior border. Upper surface convex, declining to the anterior side, and having an 

 obtuse carina on the single inter-ambulacrum ; anteal sulcus wide and deep ; the pairs of 

 petaloid ambulacra unequal in length, and forming deep depressions on the upper surface, 

 periprocte oval, opening high on the border. Ambulacral summit excentral, posterior to- 

 the disc. 



Dimensions. — A. Height, ly^ths inch ; long., l-^-ths ; lat, ly^-ths. 



B. Height ?; long., l-^jths; lat., l^ths. 



C. Height, -j^ths ; long., 1^-ths; lat., l^jths. 



D. Height, 1; long., 1-^ths; lat., l^jths. 



Description. — I have given the dimensions of four typical specimens of this Urchin 

 to show its relative proportions. A, the figured specimen, belongs to the British Museum, 

 and B, C, D are in my cabinet. A is a very globose form, and B and C are fair types. 

 In all the specimens the test is very well preserved, and there is no trace of a peripetalous 

 fasciole on any one of them, so I have removed it from the Hemiasters and placed it in 

 the genus Echinospatagus. 



Professor Edward Forbes studied the specimens of this Urchin in the British Museum,, 

 and recorded his measurements in the following memorandum. Further, he noted that 



36 



