FROM THE CORAL RAG. 



283 



of the upper surface of the single inter-ambulacrura ; base concave ; mouth opening 

 snaall, peristome equally decagonal, apical disc large, composed of unequal-sized genital 

 plates ; the right antero-lateral very large, and extending backwards beyond the centre ; 

 ocular plates small, eye-holes marginal. 



Dimensions. — In the following table I have given the dimensions of four English 

 specimens from different localities enumerated in this article, and have added the measure- 

 ments of M. Cotteau's urchin from Chatel-Censoir. 



Pygaster umbrella, Agass. 



1 



Height. 



Transverse 

 diameter. 



Antero-posterior 

 , diameter. 



Length of discal and 

 anal opening. 



Inches. 



Inches. 



Inches. 



Inches. 



Specimen from Malton 



„ ,, Headington 

 „ ,, Lyneham 

 „ ,, Farringdon 

 „ ,, Malton . 

 „ „ Chatel-Censoir 



2 



4i 

 4i 

 3 



9 R 

 9 7 



•no 



4tV 

 4tV 



2^ 



If 

 indeterminable 



u 

 If 



Description. — The greatest confusion exists regarding the synonyms of this species. 

 MM. Agassiz, Desor, and Cotteau, who have each figured and described this urchin, cite 

 Galerites umbrella. Lam., as its type ; now, Lamarck * does not say that he had seen the 

 fossil, but refers to "Leske apud Klein, p. 157, t. 12, and 'Encycl. Method.,' pi, 142, 

 figs. 7, 8," as the species intended. After consulting the original figure in Klein, which re- 

 presents Clypeus sinuatus, Leske, in the Dresden Museum, I do not see how such a 

 reference can be sustained, as the Clypeus in question belongs not only to a different 

 genus, but even to a distinct family of the Echinoidea. As Deslongchamps,f Defrance,| 

 De Blainville,§ and Desmoulins|| all founded their synonyms on this mistake, I have not 

 cited these authors in my list, for the obvious reason, that their references were made 

 under an erroneous impression. It is strange that MM. Agassiz and Desor, when cor- 

 recting the synonyms of the Pygasters, in their * Catalogue raisonne,' should not have de- 



* Galerites umbrella. Lamarck, 'Animaux sans Vertlbres,' torn, iii, p. 23, 1816. 



f Galerites umbrella. Deslongchamps, 'Encyclopedie methodique Hist. Nat. des Zoophytes,' torn, ii, 

 p. 434. 



X Nucleolites umbrella. Defrance, ' Diet, des Sciences Naturelles,' art. Galerites, torn, xviii, p. 87, 1825. 



§ Echinoclypeus umbrella. Blainyille, 'Diet, des Sciences Naturelles,' art. Zoophytes, tom. ix, p. 189, 

 1830. 



11 Nucleolites umbrella. Desmoulins, 'Etudes aur les Echinides,' p. 354, No. 2, 1837. 



37 



