FROM THE INFERIOR OOLITE. 27 5 



A. Species from the Inferior Oolite = 10 e Mage Bajocien, d'Orbigny. 



Pygaster semisulcatus, Phillips. PI. XIX, fig. 1 a, b, c, d, e,f, g. 



Clypeos semisulcatus. Phillips, Geology of Yorkshire, vol. i, p. 104, pi. 3, fig. 17 



(two thirds nat. size), 1829. 



— ornatus. Buckman, in Murchison's Geology of Cheltenham, 2d ed., 



p. 95, 1845. 

 Nucleolites semisulcata. Desmoulins, Etudes sur les Echinides, Tabl. Synoptique, p. 362, 



1837. 

 Pygaster semisulcatus. Agassiz, Prodrome d'une Monogr. des Echinodermes, p. 185, 



1837. 



— — Dujardin, in Lamarck's Hist. Naturelle des Animaux, 2 rae edit., 



tome iii, p. 353, 1840. 



— brevifrons. M'Coy, Annals and Magazine of Natural History, 2d series, 



vol. ii, p. 414. 



— semisulcatus. Wright, Annals and Magazine of Natural History, 2d series, 



vol. ix, p. 89, 1852. 



— — Forbes, in Morris's Catalogue of British Fossils, 2d ed., p. 88, 



1855. 



— — Desor, Synopsis des Echinides Fossiles, p. 165. 



Test sub-pentagonal, depressed, sometimes conoidal ; ambulacral areas prominent and 

 convex, with four rows of tubercles at the margin, diminishing to two marginal rows 

 above ; inter-ambulacra four times the width of the ambulacra, with from eighteen to 

 twenty vertical rows of tubercles at the margin, diminishing to two rows in the upper part ; 

 marginal fold acute, base flat, towards the centre very concave ; mouth sunk in a depres- 

 sion, peristome nearly equally decagonal ; discal opening wide, central ; anal opening 

 large, semisulcate, not contracted towards the disc, extending one half the distance 

 between the centre of the apical disc and the posterior border. 



Dimensions. — Height, one inch and a half; transverse diameter, three inches and one 

 eighth. 



Description. — I have omitted from the list of synonyms the Galerites umbrella, 

 Lamarck, because that species is clearly the Clypeus sinuatus, Leske; likewise the 

 Pygaster umbrella, Agassiz, of the ' Echinodermes Fossiles de la Suisse, 5 and of Desor's 

 'Monographic des Galerites,' inasmuch as the figures given in these works represent, 

 probably, another British species. It is extremely doubtful whether Pygaster semi- 

 sulcatus has been yet found out of the English Inferior Oolite ; it was said to have been 

 discovered in the Bajocien stage of the department of the Sarthe, but M. Cotteau informs 

 me that the specimen supposed to have been collected therefrom, turns out to be a 

 Gloucestershire fossil, which had got by mistake into a collection of Chauffbur urchins. 



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