Dr. T. Wright on the Cassidulidse of the Oolites. 297 



2. Group of Nucleolides*. 



Ambulacra petaloid; mouth subcentral, margin sometimes 

 surrounded with prominent lobes. 



Genus Nucleolites, Lamarck. 



Test oval, cordate, or orbicular, more or less tumid, sometimes 

 much depressed ; covered with small imperforate tubercles, sur- 

 rounded by a circular depression ; ambulacra petaloid on the 

 dorsal surface, forming straight narrow valleys on the base; 

 pores widely separate and united by transverse delicate lines 

 above, and placed close together in pairs, which are more widely 

 apart at the base ; mouth-opening subcentral, more or less pen- 

 tagonal, with or without marginal folds ; anal opening supra- 

 marginal, situated in a valley more or less deep formed by the 

 single interambulacral area, commencing near or at a short di- 

 stance from the apical disc ; vertex always excentral ; apical disc 

 situated near the vertex, and formed of two pairs of perforated 

 ovarial plates, and a single imperforate plate composed of one or 

 more pieces, having the spongy body attached to its surface, 

 and five small ocular plates arranged around the angles of the 

 ovarials. 



Nucleolites clunicularis, Llhwyd. 



Syn. Nucleolites scutata. Lam. Animaux s. Vert- tome iii. p. 36. 



Nucleolites clunicularis, Bronn, Lethsea Geognost. p. 282. 



scutatus, Agass. Echinoderm. Foss. Suisse, t. vii. fig. 19-21. 



p. 45. 



depressa, De Blainv. Zoophyt. p. 188. 



Spatangus depressus, Leske, ap. Klein, tab. 51. fig. 1, 2. p. 238. 

 Clypeus clunicularisy Phillips, Geol. of Yorksh. Part 1. p. 115. pi. 7. 



fig. 2. 

 Echinites clunicularis^ Llhwyd, Lith. Brit. Ichnogr. p. 48. No. 988, 



Test subquadrate in circumference, anterior border rounded, pos- 

 terior border bilobed ; upper surface convex, declining abruptly 

 anteriorly, and more gently posteriorly ; vertex excentrical, at 

 which is situated the apical disc ; ambulacra narrowly lanceo- 

 late above and converging below ; anal furrow deep, lanceolate, 

 and extending to the posterior border of the apical disc ; pos- 

 terior lobes gently tapering, not tumid; base concave and 

 grooved by the five ambulacral valleys ; mouth slightly penta- 

 gonal, and situated nearer the anterior than the posterior 

 border. 



* The group of Nucleolides comprehends eleven genera: Nucleolites, 

 Lam. ; Cassidulus, Lam. ; Catopygus, Agass. ; Pygaulus, Agass.; Archiacia, 

 Agass.; Pygorhynchus, Agass. ; Pygurus, Agass. ; Echinolampas, Gray; Am" 

 hlypygus, Agass. ; Conoclypeus, Agass. ; Asterostoma, Agass. 

 Ann, ^ Mag. N. Hist. Ser. 2. Vol.'w. 20 



