298 HYBOCLYPUS. 



It is found occasionally in the planking beds of the Great Oolite at Minchinhampton 

 Common. The Great Oolite specimens, however, are small, and not well preserved. M. 

 Deslongchamps kindly communicated a specimen which he collected from the " Oolite 

 ferrugineuse de Bayeux." On the ticket which accompanied it was written, " Seul 

 exemplaire que j'ai trouve," so that it is extremely rare in Normandy. This urchin very 

 much resembled our small common examples from the Inferior Oolite. I know it from no 

 other foreign locality. 



Hyboclyptjs gibberulus, Agassiz. PL XXI, fig. 2 a, b, c, d, e,f,g. 



Hyboclypus gibberulus. Agassiz, Echinodermes Fossiles de la Suisse, part i, p. 75, pi. 13, 



figs. 10—12. 



— — Desor, Moiiographie des Galerites, p. 84, pi. 13, figs. 12 — 14. 

 ^^ — D'Orbigny, Prodrome de Paleontologie, torn, i, p. 290, 



^tage 10% Bajocien. 



— — Bronn, Lethaea Geognostica, 3^ Aufl., tabl. 17', fig. 11. 



— — Agassiz and Desor, Catalogue raisonne, Annales des Sciences 



Naturelles, torn, vii, p. 152, serie 3°. 



— — Desor, Synopsis des Echinides Fossiles, tabl. 26, figs. 11 — 13, 



p. 192. 

 NucLEOLlTES Excisus. Quenstedt, Handbuch der Petrefactenkunde, tabl. L, fig. 3, 



p. 585. 



Test oblong, elevated above, and contracted on the sides before ; enlarged, depressed, 

 produced, and truncated behind; single ambulacral area the highest, and, with the 

 antero-lateral inter-ambvilacral areas, form a gibbous crest ; longitudinal valley wide 

 and deep ; single inter-ambulacrum slightly produced, deiflected, and truncated ; base much 

 undulated, a depression in the anterior border ; apical disc elongate, nearly central, but 

 not vertical ; vent very wide, opening at the inner extremity of the valley ; mouth opening 

 small, oblong, sub-central, near the anterior border. 



Dimensions.- — Height, nearly one inch ; transverse diameter, two inches and one tenth 

 of an inch ; antero-posterior diameter, two inches and one tenth of an inch. 



Description. — This urchin has so singular a form, that when once seen, it is not 

 likely to be mistaken for any other, being remarkable for a prominent gibbous crest 

 (fig. 2 d, e), which rises from the anterior half of the test, formed by the elevation of the 

 single ambulacral area, and the two anterior inter-ambulacral areas ; from the anterior 

 border to the mouth a depression extends (fig. 2 h, d); the anterior lateral are more 

 contracted than the posterior lateral borders (fig. '2j a, h); the posterior half of the test 



