266 Dr. T. Wright on the Cidaridse of the Oolites, 



poriform plate is rudimentary, to make space for the apex of the 

 anal opening. By this arrangement it is evident that the anus is 

 eccentrical and situated behind the sur-anal plate ; its opening is 

 in a great measure formed by the imperfect development of the 

 madreporiform plate, a condition the opposite to that existing in 

 A. hemicidar aides, where the anus is situated in front of the sur- 

 anal plate, and is excavated at the expense of the left anterior 

 ovarial plate. The four ovarial and sur-anal plates are adorned 

 with a delicate sculpture which occupies their centres ; the ocular 

 plates are small ; the three anterior are inserted between the pro- 

 minent angles of the ovarials, whilst the two posterior lying be- 

 tween the madreporiform plate and the posterior pair of ovarials 

 form the lateral walls of the anal opening; all the plates are 

 finely granulated. 



The mouth is large, its circumference being divided into ten 

 nearly equal lobes, and the margin is much retiexed. 



Affinities and differences. — Aa-osalenia spinosa is distinguished 

 from its congeners by its subpentagonal form, the volume of the 

 - mammillary eminences of the primary tubercles at its equator, 

 and the sudden smallness of those occupying the upper part of 

 the test, the position of the anal opening behind the sur-anal 

 plate, and the rudimentary condition of the madreporiform plate. 



Locality and stratigraphical range. — I collected this Urchin 

 from the yellow clay resting on the Stonesfield slate at Seven- 

 hampton with Anabacia orbulites, Pecten vagans, Ostrea acumi- 

 nata, and other Great Oolite shells. Likewise from the Corn- 

 brash near Chippenham, Wilts, where it is very abundant. The 

 specimens from both localities are as perfect as recent Echini. 



Many of the Cornbrash specimens are attached to Avicula 

 echinata. In Switzerland A. spinosa was collected from marls 

 containing Ostrea acuminata in the Canton of Soleure. It is 

 found in great abundance in France in the Great Oolite of Caen, 

 and has been collected by M. Cotteau fi'om the upper beds of the 

 Bathonian stage in the environs of Chatel-Censoir. 



History. — This species was figured and described for the first 

 time by M. Agassiz in his ^Echinoderra. Fossiles de la Suisse,' 

 and entered in his 'Catalogue raisonne des Echinides.' It has been 

 figured and described by M. Cotteau from specimens obtained 

 in the department of FYonne. It is catalogued by Mr. M'Coy 

 as a Minchinhampton species from the Great Oolite, and is now 

 described from British specimens for the first time. 



Genus Goniopygus, Agassiz. 



Test circular, subconical ; apical disc very solid with an angular 

 circumference, composed of ten plates ; sur-anal plate absent ; 

 mouth large ; tubercles imperforate without crenulations at their 

 base ; pores disposed in simple pairs throughout. 



