1G6 Dr. T. Wright on new Species of Echinodermata 



in M. Agassiz's ' Catalogus Systematicus* ' as Hemicidaris minor, 

 from specimens sent to him by M. Michelin ; it afterwards found 

 a place in the ' Catalogue raisonne des Echinides ' of Agassiz and 

 Desor, accompanied with this remark : " Se distingue entre tous 

 les Hemicidaris par les tubercules tres espaces, dont il n^y a que 

 deux out rois dans une rangee. — Terrain Jurassique de France. — 

 Michelin." Professor M'Coy, in his paper '"'On some new Me- 

 sozoic Radiatat," afterwards described this Urchin under the 

 name Acrosalenia rarispina, giving the Great Oolite of Minchin- 

 hampton for its locality. As that gentleman has kindly favoured 

 us with pen-and-ink sketches of the species described as new in 

 that paper, we have no difficulty in deciding on the identity of 

 his specimen. Moreover we have ascertained the collection from 

 whence it originally came. The error committed by this learned 

 author in the genus must have arisen from the disc; in his spe- 

 cimen having been covered with "adhering siliceous matrix," 

 and from his having overlooked the very remarkable character 

 pointed out by Agassiz, " les tubercules tres espaces." We have 

 been fortunate to receive a typical specimen of the original spe- 

 cies from the Great Oolite of Langrune, through the kindness 

 of our friend Professor Deslongchamps ; we have compared the 

 French Urchin with specimens obtained from the same locality 

 as that from whence Prof. M'Coy's was collected; and there is not 

 a shadow of a doubt about their perfect identity. We have 

 figured in detail this beautiful and singular form, to prevent the 

 possibility of mistakes occurring about it in future. 



This pretty little Hemicidaris is very distinct from all others of 

 the group to which it belongs : the test is nearly hemispherical, 

 and the few primary tubercles stand prominently at great di- 

 stances apart from the surface of the test. The narrow ambulacral 

 areas are slightly flexuous above, and have from four to six large 

 perforated tubercles at their base only, the sides and upper part 

 of the areas having first four, and then two rows of small imper- 

 forate granules upon their surface about equal in size to the gra- 

 nulation which covers other parts of the test. The poriferous 

 avenues are depressed, and the pedal pores are disposed in pairs 

 throughout. The interambulacral areas depart considerably from 

 the typical structure of this portion of the test in other Echinidse ; 

 they are three times the width of the ambulacra, and have at 

 their base three large primary tubercles, two on one side and one 

 on the other, with a smaller tubercle above the single large one ; 

 on the sides and upper part of the areas there are only three 

 primary tubercles, two on one side and one on the other, making 



* Catalogus Systematicus Ectyporum Echinodcrm. Foss. Mus. Neoco- 

 mensis, 1840. 

 t Annals of Katural History, 2nd Series, vol. ii. p. 111. 



