FROM THE INFERIOR OOLITE. 377 



Affinities and differences. — The general outline of some of the smaller specimens of this 

 urchin resembles Echinobrissus orbicularis, but the structure of the ambulacra, and of 

 the apical disc, the size and position of the anal valley, together with the undepressed 

 portion of test between the apex of the valley and disc, readily distinguish it. The 

 larger form (fig. 1 a) differs so entirely from other Clypei that it cannot be mistaken 

 for any of its congeners, whilst its orbicular outline, petaloidal ambulacra, small 

 solidified apical disc, and mouth-opening provided with oral lobes, justify its position 

 among the Clypei rather than with Echinobrissus, among which I formerly placed it. 



Locality and Stratigraplncal position. — I have collected Clypeus Iluyii in the Lower 

 Trigonia Grit, zone of Ammonites Parkinsoni Inferior Oolite, at Rodborough Hill, 

 Shurdington Hill, Leckhampton Hill, and Ravensgate Hill ; the large figured specimen 

 was found at Shurdington Hill. I have collected many specimens from the Trigonia 

 Grit at Hampen ; many years ago it was found in considerable abundance in the upper 

 ragstones of the Inferior Oolite with Triyonia costata at Charlcombe, near Bath. The 

 Hampen specimens are associated with Pedina rotata, Wr., Hyboclypus ovalis, Wr., 

 Ilolectyjms depressus, Lamk., and Clypeus Plotii, Kl., with several species of Conchifera 

 characteristic of that zone of life, as Triyonia costata, Sow., Pecten symmetricus, Mor., 

 Tancredia donaciformis. Lye., and Quenstedtia oblita, Phil., together with Anthozoa, as 

 Anabacia orbulites, Lamx. 



The foreign distribution of Clypeus Iluyil, is, according to M. Desor, " Marnes a 

 Discoides (Vesulien), de Hornussen et de Bozen (Argovie), des environs d'Olten, du Mont 

 Terrible." 



In Switzerland, he adds, this species is the faithful companion of Holectypus depressus. 

 Colly rites ovalis, and Echinobrissus clunicularis, and one of the most characteristic 

 fossils of the Marnes a Discoides, the zone of Ammonites Parkinsoni Inferior Oolite, so 

 that its statigraphical position and palseontological associates is the same in the Alpine 

 regions of Switzerland, as in the Cotteswold Hills. 



The true zone of this species in the department of the Sarthe is yet uncertain, the 

 only specimen found was collected near Mamers. I have no doubt its bed will be found to 

 be the Inferior Oolite. 



