from the Lias and Oolites. 323 



all the specimens we have examined ; the interambulacral areas 

 are of unequal width, the antero-lateral pair are the narrowest, 

 they are however about nine times the width of the anterior 

 single ambulacral area ; the postero-lateral pair are /yths of an 

 inch wider than the antero-laterals, and the single interam- 

 bulacrum is about the same width as the latter. The anal valley 

 extends from the apical disc to the posterior border ; it is very 

 narrow, with deep perpendicular sides above, which become shal- 

 low and expanded below ; the postero-lateral interambulacra are 

 swollen out at the margin; the single interambulacrum is 

 considerably produced, and its posterior border is broadly trun- 

 cated and slightly deflected, within which the expanded sides of 

 the anal valley are excavated. The base is nearly flat, the eleva- 

 tions are due to the prominence of the postero-lateral interam- 

 bulacra, and to the deflection of the single interambulacrum. 

 The mouth is excentral, nearer the anterior margin, and the oral 

 lobes are small ; the apical disc was of moderate size, judging 

 from the space it occupied, but it is absent in all our specimens ; 

 the surface of the test was covered with very minute tubercles, 

 which in the examples before us are nearly all efiaced. 



Affinities and differences. — N. Michelini in its oblong form, 

 truncated posterior margin, and narrow anal valley resembles 

 N. Solodurinus, but it is readily distinguished from it by the 

 form, narrowness, and structure of the ambulacral areas ; in 

 N. Solodurinus they are expanded and petaloid, and in N. Miche- 

 lini they are narrow and lanceolate ; the pores at no point are 

 at any great distance apart ; the anal valley in both species ex- 

 tends from the apical disc to the margin, but it is more expanded 

 below and deeper above in N. Michelini than in N. Solodu- 

 rinus. We have before us Clypeus angustiporus, Agass., from 

 a coarse Oolitic rock (Bradfordien ?) near Metz, collected by 

 M. Terquem, and kindly sent us by M. de Loriere; from this 

 species N. Michelini difiers in many particulars ; in the French 

 Urchin the apical disc is excentral, the anal valley is wide above 

 and not much expanded below, the ambulacral areas are narrow, 

 and the test gradually declines from the vertex to the anterior 

 border, which forms a rather acute angle ; the base is undulated, 

 and the mouth-opening is nearly central ; these characters clearly 

 distinguish our Urchin from it. N. Michelini difi'ers so widely 

 from all the various varieties of N. sinuatu^ with which we are ac- 

 quainted, that it cannot possibly be mistaken for either of them, 

 if any care be taken when a comparison is made between them. 



Locality and stratigraphical range. — We have collected this 

 species only from the Freestone beds of the Inferior Oolite of 

 Wallsquarry and Nailsworth ; the specimen figured was cut out 

 of the centre of a block of building stone ; the oolitic grain.^ are 



21* 



