Dr. T. Wright on the Cassidulidae of the Oolites. 215 



species. The base is concave and undulated, the ambulacra 

 forming straight valleys, and the interambulacra more convex 

 elevations than in any other of its congeners. The mouth is very 

 excentral, being situated near the junction of the anterior with 

 the middle third of the basal anteroposterior diameter ; the 

 opening has a pentagonal form, and is surrounded with five 

 small lobes. The apical disc occupies the vertex, which is slightly 

 excentral, inclining towards the posterior border ; it is formed of 

 two anterior and two posterior perforated ovarial plates with a 

 single imperforate plate and a spongy madreporiform body oc- 

 cupying the centre ; the ocular plates are small, and the orbits 

 appear to be formed by the apices of the ambulacra and the 

 margin of the ocular plates. The test is moderately thick, its 

 surface is closely covered with small tubercles surrounded by a 

 circular depression, and the intertubercular spaces are delicately 

 sculptured with microscopic granules ; the tubercles on the dorsal 

 surface are much smaller than those on the base. 



Affinities and differences. — This species resembles N. orbicu- 

 laris in its suborbicular form, but is readily distinguished from 

 that species by its declining sides and the absence of the general 

 tumidity so characteristic of N. orbicularis ; the form and structure 

 of the anal valley are likewise different ; in N. orbicularis it extends 

 from the margin to the apical disc, whilst in N. Hugii it occu- 

 pies only the inferior half of the single interambulacrum ; that 

 area is likewise more produced and much deflected in N. Hugii, 

 From N. dimidiatus, N. Hugii is readily distinguished by the in- 

 ferior position of the anal opening, the deflected lip-like form of 

 the single interambulacrum, and the rudimentary condition of 

 the posterior lobes ; the size and suborbicular outline of N. Hugii 

 form likewise a strong contrast to the small oblong form of 

 N. dimidiatus. 



Locality and stratigraphical range. — I have collected N. Hugii 

 from the Inferior Oolite of Rodborough Hill, and a mutilated 

 specimen from the upper ragstones of Leckhampton Hill ; it is 

 therefore a rare Urchin in Gloucestershire. Its foreign distri- 

 bution, according to Agassiz, is Inferior Oolite du Jura Soleurois 

 et Eveche de Bale, le Mont-Terrible (Cant, de Berne). As far 

 as I can learn, it has hitherto been found only in the Inferior 

 Oolite. 



History. — First figured and described by Agassiz in his ' Echi- 

 nodermes Fossiles de la Suisse/ identified in the British Mu- 

 seum collection as a British Urchin by Mr. S. P. Woodward, 

 enumerated in Prof. Forbes's note on a British Nucleolites" and 

 now described in detail as such for the first time. 



