300 HYBOCLYPUS. 



gives a faithful representation of the disc) ; the anterior are smaller than the posterior 

 ovarials ; the right is larger than the left plate, and supports, as usual, a spongy madre- 

 poriform body ; the posterior ovarials are large and elongated, and separated from the 

 anterior pair by the excessive development of the anterior pair of ocular plates, which form 

 an important part of the disc ; the large oviductal holes always indicate the true relative 

 position of the genital plates ; the single imperforate ovarial is composed of two plates, 

 placed end to end, and behind the posterior ovarials the posterior pair of ocular plates 

 are placed. M. Desor's figure of the disc of this species does not agree with our speci- 

 mens, as the single imperforate ovarial, which is central and double, is entirely wanting 

 in his figure, probably through an oversight on the part of the artist. I have verified 

 Mr. Bone's beautiful drawing in three different individuals by a careful examination with 

 the lens. 



Affinities and differences. — This remarkable urchin, which formed the type of the 

 genus, is so well characterised by its gibbous crest that it cannot be mistaken for any 

 other species. H. ovalis has a considerable resemblance to it ; but the absence of the crest, 

 its oval form, and the want of those prominent traits which distinguish H. gihherulus, 

 clearly distinguish them from each other. 



Locality and StratigrapMcal position. — I have collected this species in the upper beds 

 of the Inferior Oolite, in the zone of Ammonites Farkinsoni, Sow., at Burton Bradstock, 

 and Walditch Hill, near Bridport, Dorset ; a few specimens have been found in the Inferior 

 Oolite in the parish of Charlcomb, near Bath. The Dorsetshire specimens were associated 

 with Holectypus hemisphcericus, Desor, Stomeclnnus hiyranularis, Lamk., Clypeus altus, 

 M'Coy, CoUyrites ringens, Agass., Terehratula splicer oidalis, Sow., Bhynchonella plicatella. 

 Sow., Terehratula Phillipsii, Mor., Ammonites Farkinsoni, Sow., Ammonites sub-radiatus. 

 Sow. 



It appears to be a rare species on the Continent. M. Desor observes, " Suivant les 

 indications que m'a fournies M. Grossly, on la trouve dans une couche particuliere de 

 rOolite inferieure, la marne a Ostrea acuminata, la merae qui contient aussi Fiscoidea 

 {Holectypus) depressa, et le Fysaster analis, c'est au moins dans cette couche que I'a 

 rencontree M. Strohmeyer." "*' In his 'Synopsis des Echinides Fossiles,' M. Desor gives, 

 as the other foreign locahties of this species, "Vesulien (Marnes a Discoidees du Jura 

 Soleurois et Argovien, du Hummel, pres Waldenburg. Grande Oolite tie Macon (Hebert), 

 du depart, de I'Ain." 



M. De Loriere has sent me a specimen which he collected at " Nogent, etage Callovien, 

 departement de la Sarthe ;" and from M. Ssemann I have received another from the 

 etage Callovien of the same department. I have already expressed a doubt as to the age 



* ' Monographic des Galerites,' p. 85. 



