PLEIOCENE FOSSILS. 9 



and deep groove, the others in shallower ones. Below, we find the breast-plate very broad 

 and every where the shell appears to have been studded with numerous, crowded knops, 

 relatively smaller in size than those of the Cuban species. 



This description is taken from an imperfect cast, (an upper view of which is given, Plate 

 III., fig. 1,) and several fragments, one of which, a breast-plate, is figured on the same Plate, 

 fig. la. The cast was found by Dr. Edmund Ravenel, and noticed by him in his Catalogue 

 as Pericosmus spatiosus, with the remark that when more data should be obtained, it would 

 probably be necessary to remove it from that genus. Having enjoyed, through the kind- 

 ness of Dr. Ravenel and Prof. Agassiz, an opportunity of more accurately determining its 

 generic characters, I remove it to the genus Brissus. It is intended also to give a mono- 

 graphic account of the remains of this and the two following species, in an appendix to 

 appear at a later day. 



Plate III., Fig. 1. Upper view of cast. There remain only partial impressions of two Ambulacra, 



the odd one, and the left limb of the first pair. 

 " la. A breast-plate, with part of the hinder ambulacrum of the left side. 

 " lb. Enlarged hnops, with their characteristic pentagonal shield, from a fragment of 



the lower surface. 

 " lc. Profile view of another hnop of the same kind. 



Locality. The Grove, Cooper River, S. C. (J. McC.) 



PLAGIONOTUS.— Agassiz. 

 PLAGIONOTUS HOLMESIL— McCkady. 



Plate III., Fig. 2, 2a. 



Fragmenta quae Plagionotum P. pectorali valde similem indicant, et jugis descendentihus 

 inter ambulacrorum paris posterioris^ modice appropinquatis • fasciola peripetali non antice 

 duplicata. Probabile est — quod, animalis forma valde ovalis, et latafuit. 



This species is indicated by numerous fragments in our Pleiocene. It approached most 



nearly to the species figured by Seba and copied by Lamark, who gave the name, Spatangus 



pectoralis. — (Brissus (Plagionotus) pectoralis. — Ag.) The plate-ridges of the second 



pair of interambulacra are somewhat closely approached and the outer star-belt is not 



3 



