FROM THE INFERIOR OOLITE. 301 



of the beds which have yielded Hyboclypus gibberulus, Pygurus depressus, and Collyrites 

 ringens, in the department of the Sarthe ; my friend M. Cotteau is at this moment 

 engaged on a work on the Echinoderms of that department, and my friend M. Triger 

 has undertaken a review of the stratigraphical distribution of the species. From this 

 monograph Ave shall therefore learn the true age and position of these strata. 



History. — This species was first figured and described by M. Agassiz, in his 

 ' Echinodermes Fossiles de la Suisse,' he only knew two specimens from the Inferior Oolite 

 of Switzerland. It was afterwards figured by M. Desor in his valuable ' Monograph 

 on the Galerites/ and was described by me as a British fossil for the first time.* It has 

 lately been figured by M. Bronn in his ' Lethaea Geognostica,' and by M. Desor in 

 his ' Synopsis des Echinides Fossiles.' 



Hyboclypus ovalis, Wright, nov. sp. PI. XXII, fig. 1 a, b, c, d, <?,/. 



- Test oval or suborbicular, upper surface convex, rather more elevated anteriorly; 

 ambulacral areas narrow, nearly of equal width ; the single and anterior pair straight ; 

 posterior pair curved gently upwards, inwards, and forwards ; apical disc small, nearly 

 central, rather nearer the anterior border; longitudinal valley of moderate width and 

 depth ; base concave and undulated, from the convexity of the basal inter-ambulacra ; 

 mouth opening small, excentral, nearer the anterior than the posterior border. 



Dimensions. — Height, seven tenths of an inch ; transverse diameter, one inch and 

 eleven twentieths ; antero-posterior diameter, one inch and thirteen twentieths. 



Description. — This species very much resembles H. gibberulus, but it wants the striking 

 features of that urchin ; the contracted anterior border, expanded posterior border, wide 

 anal valley, and prominent gibbous crest are absent ; although in the minute structure of 

 the test there is much resemblance between them. It is collected, moreover, from the same 

 stratigraphical horizon, the zone of Ammonites Parkinsoni, Sow., and may be regarded as 

 the representative of H. gibberulus in the Cotteswold Hills, as that species, so far as 

 I know, has never yet been found in this district. 



The test is in general oval, but it has sometimes a sub-orbicular shape (fig. 1 a). 

 The upper surface is very uniformly convex, and the anterior part is rather more elevated 

 than the sides (fig. 1 c) ■ most Hyboclypi manifest a disposition to the formation of 



* ' Annals and Magazine of Natural History,' 2d series, vol. ix, p. 120. 



