Dr. T. Wright on the Cassidulidse of the Oolites. 303 



Nucleolites Hugii, Forbes. 



Syn. Clypeus Hugi, Agassiz, Echiu. Foss. Suisse, vol. i. p. 3 7. tab. 10. 



fig. 2-4. 

 Nucleolites Hugii, Forbes, Mem. Geol. Surv. Decade 1. description 



of pi. 9. 



Test suborbicular, dorsal surface convex and depressed ; apical 

 disc and vertex subexcentral ; ambulacra lanceolate, apices ap- 

 proximated; anal valley oblong, obtuse and short, separated 

 from the vertex by a considerable portion of undepressed test ; 

 single interambulacrum produced and much deflected ; poste- 

 rior lobes small ; base concave and undulated ; mouth much 

 excentral near the anterior border, of a pentagonal form and 

 surrounded by five lobes. 



Height |^ths of an inch, antero-posterior diameter 1 inch and 

 jjyths, transverse diameter the same as the antero-posterior. 



Description. — This is a very distinct form of Nucleolite ; the 

 circumference is suborbicular, sometimes a little compressed at 

 the sides ; the dorsal surface is convex, and the antero-posterior 

 exceeds the transverse diameter in some, and these diameters are 

 nearly equal in other individuals. The ambulacra have a lanceo- 

 late form ; the single ambulacrum and the anterior pair are nearly 

 the same width, and the posterior pair are the widest; their 

 apices approximate very closely in consequence of the smallness 

 of the apical disc. The pores are not far apart on the dorsal 

 surface ; the internal row consists of small round holes, the ex- 

 ternal row are somewhat elongated transversely, and unite with 

 the internal row by a delicate suture ; near the border they ap- 

 proximate and are disposed in close-set pairs. As we trace them 

 from the basal angle to the mouth they he widely apart, but 

 near the mouth they become again more closely approximated, 

 and fall into triple oblique pairs as in Echinus and Pedina. The 

 anterior pair of interambulacra are the narrowest, the single in- 

 terambulacrum is the widest, and the posterior pair are of inter- 

 mediate dimensions ; the anterior border is obtusely rounded, the 

 sides swell gradually outwards to the junction of the posterior 

 pair with the single area, which is the widest part of the test ; 

 the single interambulacrum is slightly produced and much de- 

 flected ; the anal valley is short and oblong, with an obtuse up- 

 per margin, which does not extend one half the distance between 

 the border and the vertex, the space between the anal margin 

 and the vertex being occupied by a smooth undepressed portion 

 of the test : this character allies N. Hugii to N. dimidiatus ; but 

 the orbicular outline, the greater size, and the produced and de- 

 flected single interambulacrum of the former constitute a group of 

 characters by which it is readily distinguished from the latter 



