380 CLYPEUS 



characters which well characterise this noble urchin ; in the fine large specimen figured by 

 my friend M. Cotteau from the Inferior Oolite of the Sarthe, a narrow sulcus extends 

 from the disc to the summit of the anal arch. 



The mouth-opening is large and sub-central (PI. XXXI, fig. 1 (5) ; it has a pentagonal 

 form, and the peristome is surrounded by five large, prominent, oral lobes, formed by the 

 terminal folds of the inter-ambulacra; alternating with the lobes, the five ambulacra 

 form a depressed penta-phylloid floscule around the mouth opening, which imparts a 

 marked stellate character to the flat base of this Clypeus. 



Affinities and differences. — This fine species is distinguished from its congeners by its 

 elevated, sub-conoidal, dorsal surface, its flat base, its excentral apical disc, declining 

 towards the posterior border, its short, shallow, anal valley, and oblong vent. In some 

 specimens the anal valley is more developed than in our large flne type urchin ; this is 

 apparent in two other individuals I possess, and M. Cotteau has made the same remark 

 on some of the specimens which he has examined from the Sarthe : " Suivant, M. Wright, 

 cette ouverture est a fleur du test, presque superficielle {nearly superficial). Ce caractere 

 n'existe pas toujours, et dans plusieurs de nos exemplaires, notamment dans celui que 

 nous avons fait representer, I'anus s'ouvre dans un sillon aigu, au milieu d'une depression 

 tres-apparente de I'inter-arnbulacre-posterieur ; mais cette difference ne nous a pas empeche 

 de le reunir au Clypeus Agassizii. Les echantillons d'Angleterre pr6sentent eux-memes 

 quelques traces de sillon et appartiennent certainement au meme type que les notres." * 



Locality and StratiyrapMcal position. — This urchin has hitherto been found only in the 

 upper ragstones of the Inferior Oolite, near Bridport, in the zone of Ammonites 

 Parkinson!, at Barton-Bradstock, and Walditch Hill ; its associates in the same bed are 

 Clypeus alius, M'Coy; Holectypus hemisphcericus, Desor; StomecJdnus biyranularis, 

 Lamk. ; Collyrites rinyens, Desml. ; Collyrites ovalis, Leske ; Hyhoclypus yibberulus, Ag. ; 

 Ammonites ParMnsoni, Sow. ; Ammonites suhradiatus. Sow. ; Trigonia costata. Sow. 



History. — ^Pirst figured and described in my memoir on the Cassidulidse of the Oolites 

 'Ann. and Mag. of Nat. Hist.', for 1851. It has recently been beautifully figured and 

 well described by MM. Cotteau and Triger, in their fine monograph ' on the Echinides' of 

 department of the Sarthe. 



* Cotteau and Triger, Echinides du departement de la Sarthe, p. \7, 1858. 



