130 Prof. P. M. Duncan and Mr. W. P. Sladen on 



Edward Forbes considered the genus Peltastes, Agass., to 

 be of doubtful value, and believed that it was a section or sub- 

 genus of Salenia. There is much to be said in favour of this 

 view ; but it must be admitted that there is equal reason for 

 regarding Salenia as a subgenus of Peltastes. But the 

 species of Peltastes as a whole are older geologically than those 

 of Salenia, and the generic distinction is the presence of a 

 dorso-central plate in the antero-posterior axis of the apical 

 system and of a periproct which is placed posteriorly to the 

 dorso-central plate in Peltastes, and not to the right posterior, 

 as occurs in Salenia. In all other important structures there 

 is no morphological distinction to be made, although there are 

 distinctions to be drawn regarding the ornamentation. The 

 only satisfactory argument which can be advanced against 

 the combination of the two types is that the species of each 

 are numerous and definite, and that the Peltastes are extinct. 

 The two groups are not connected by any intermediate species. 

 We retain the genus Peltastes after indicating the very close 

 affinity with Salenia and the probability of the last-named 

 being a descendant of the first. 



Genus Peltastes, Agassiz, 1838, Monogr. des Salenies ; 

 amended in Catal. raison. Ann. des Sci. Nat. 1846 (non 

 Desor, Synopsis, p. 145). 



Test small, circular in outline, tumid at the ambitus, 

 depressed and slightly tumid abactinally, or tall, with a 

 part of the apical system projecting, actinally rather flatly 

 curved. Apical system large, raised slightly, and part of it 

 usually projecting, with large basals and small radials j a 

 dorso-central plate small, in the long axis of the system, united 

 to the basals 1 to 4, but not touching the basal 5, curved 

 posteriorly for the anterior margin of the periproct. E,adials 

 large, not within the ring. Periproct posterior, bounded 

 in front by the dorso-central plate and posteriorly and laterally 

 by the basals 4, 5, and 1. The sutures of the disk often 

 grooved, marked with depressions and the prolongation of the 

 ornamentation of the basal and dorso-central plates ; these 

 plates with grooves and eminences often radiate in arrange- 

 ment, margins of the basals often variously curved and notched. 

 Ambulacra narrow, straight or slightly flexuous, with small 

 primaries near the poriferous zone ; plates low primaries only. 

 Interradia with large primary tubercles at the ambitus, dimi- 

 nishing in size above and below, crenulate and usually im- 

 perforate. Peristome small, rather reentering, slightly incised. 



