ECHINOIDEA EXOCYCLICA. 189 



tlieir outer third b}' a large ovidnctal hole ; the madreporiform tubercle is feebly developed 

 and occupies the inner portion of the right antero^lateral plate ; in most specimens the 

 ocular plates are small and angularly reniforra, the orbit is excavated out of the centre of 

 their outer margin, the elements of the disc are covered with numerous small granules, 

 which are closely crowded together on the surface of all the plates. 



The test' is extremely thin, and the spines are at present unknown. 



Affinities and Differences. — There are very few species in the genus Cottaldia. C.conica, 

 Agass., is merely an elevated form of C. gramdosa ; C. BucJdi, Steiniger, is a nearly 

 allied species, from a Tertiary rock at Rommelsheim, near Friim. 



Loccdity and Stratigraphical Position. — This Urchin was formerly very abundant in 

 the Upper Greensand of Warminster, and at Chute Farm, Wilts. On the Continent the first- 

 described specimens were collected at Regensburg, Bavaria. In France, according to M. 

 Cotteau, it is found at Villers-sur-mer (Calvados) ; le Havre, Rouen (Seine- Inferieure) ; 

 Yimoutiers, La Perriere (Orne) ; La Madeleine (Eure) ; le Mans, Coulaine, Yvre-l'Eveque, 

 les Bordiers, Nogent-le-Bernard, Gaville (Sarthe) ; Cherves-de-Cognac (Charente- 

 Inferieure) ; La Bedoule (Var) ; very abundant in the Etage Cenomanien = Upper 

 Greensand ; Environs of Royan (Charente-Inferieure) ; very, rare in the Etage Senonien 

 :=. Low-er Chalk. . 



ECHINOIDEA EXOCYCLICA, Wright, 1855. 



Before entering upon the study of the Echinoidea exocyclica, it is due to the 

 Echinological student to state in general terms the reasons that have led to the adoption 

 of names for several generic groups so different from those in general use at the present 

 time. In working out the materials for these Monographs it has been my most earnest 

 endeavour to do justice to my predecessors and contemporaries in the same field of labour, 

 by observing the most scrupulous care in reference to priority of date in each 

 genus and species founded on figures or descriptions, or both; without a rigorous 

 base of equity on this fundamental principle, it would be vain to hope for the stability of 

 any sysjtem of nomenclature, or limits to the interminable list of synonyms which would 

 result from its neglect. In every case, therefore, I have traced back the history of each 

 genus and species to its original author, and have added his name and the date after 

 each, so that justice is done to every naturalist who has enriched our science by original 

 work. The following remarks were made in the preface to my Monograph on the Oolitic 



