Dr. T. Wright on the Cidaridse of the Oolites. 85 



natural relations of the species ; it is formed of an anterior and 

 a posterior pair of moderately- sized ovarial plates, and a rudi- 

 mentary single ovarial plate. The sur-anal plate is very curious, 

 and is composed of two unequal-sized pentagonal pieces united 

 with the anterior and posterior ovarials, and six small pieces 

 forming an arch which spans from the^ right to the left 

 posterior pair of ovarials, and forms the anterior border of 

 the anus ; the posterior pair of ocular plates forms the lateral, 

 and the single rudimentary ovarial plate the posterior boundary 

 of the anal opening, which is transversely oblong, slightly 

 excentral, and consequently placed behind the compound sur- 

 anal plate. The ocular plates are heart-shaped and of a mo- 

 derate size, and their eyeholes are very minute. The surface of 

 the discal plates is covered with small granulations. The tumid 

 sides are gently rounded towards the base. The mouth-opening 

 is small, being rather more than one-third the diameter of the 

 test ; its margin is decagonal, with nearly equal-sized lobes, those 

 of the ambulacra being the widest. The fragment of a primary 

 spine before me is cyhndrical and smooth, and judging from its 

 thickness must have been long. The secondary spines are short, 

 -prickle-shaped, and sculptured with fine longitudinal lines (4e). 



Affinities and diffe?'ences. — The preservation of the apical disc 

 proves that the natural affinity of this species is with A. spinosa 

 and A. decor ata, whilst in the general form and structure of the 

 test, A. Wiltonii most resembles A. hemicidaroides ; but it differs 

 from that species in having the anal opening behind the sur-anal 

 plate, whereas in A. hemicidaroides it is situated before it. 



Locality and stratigrapkical range. — This Acrosalenia was col- 

 lected from the Cornbrash near Sutton Benger, Wilts ; it appears 

 to be rare. I dedicate this species to my friend John Wilton, 

 Esq., of Gloucester. 



Echinus gyratus, Agassiz. 



Syn. Echinus gyratus^ Echin. Foss. de la Suisse, part 2. p. 87. 



tab. 23. fig. 43-46. 

 Echinus petallatus, M'Coy, Annals Nat. Hist. vol. ii. p. 409, 2nd 



Series. 



Test hemispherical, more or less elevated, with an orbicular cir- 

 cumference, divided into fifteen slightly convex lobes ; ambu- 

 lacral arese half the width of the interambulacral, with two 

 complete rows of marginal tubercles extending from the 

 mouth to the apical disc, and two incomplete rows of central 

 tubercles occupying about two-thirds of the sides thereof ; in- 

 terambulacral arese with a smooth concave median space ex- 

 tending from the disc to near the basal angle ; each of the 

 two lobes formed thereby has one complete central range of 



