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



show the depressions first noticed by Cotteau. The ambu- 

 lacra are very narrow, and the tubercles are small and 

 crowded actinally ; the pores are rather large, and the pairs 

 are environed by a peripodium with a narrow linear and raised 

 edge ; the ambulacral j^lates are low primaries, and there are 

 no compound plates. The depressions are deep and more or 

 less circular in outline, and the}' are evidently in the line 

 of suture between contiguous ambulacral plates ; and, as the 

 tubercles (not granules) are crowded and sometimes nearly 

 cover the sutures, the position of the depressions is at the base 

 of a tubercle, or where a tubercle might have been. Really 

 the depressions are pits in the line of suture and somewhat 

 resemble the deep groovings of the Temnopleurida3 ; but there 

 are no deep and large pits at the angles of the plates as in that 

 family. 



The pits are confined to the surface below the ambitus and 

 get crowded near the peristome. The specimens examined by 

 us do not show any pores on the floor of the pits, but, on the 

 contrary, where any structure is to be seen it is of a nature 

 indicating the a))pearance of the former presence of articular 

 tubercles of spha^ridia. We consider that as the principal cha- 

 racters of Peltastes are present in the species, they must come 

 under a subgeneric group. 



Subgenus GoniophoruSy Agassiz (genus), 1838. 



Test small, swollen, subspheroidal, with large peristome, few 

 interradial primaries, plain and crenulated. Apical system 

 pentagonal, with five basals and five small radials ornamented 

 with linear and raised straight keels not on the lines of the 

 sutures ; a dorso-central plate ; periproct posterior to it and 

 elongate transversely. Pits for sphseridia large in the narrow 

 ambulacra actinally. 



Distribution. Fossil : England, Europe ; Upper Green- 

 sand. 



The genus Peltastes therefore has as its synonyms Pseudo- 

 salenia and Hyposalenitty and there is a subgenus Oonio- 

 phorus. 



Genus Salenia. 



The genus Salenia, Gray, Proc. Zool. Soc. Lond. 1835, 

 p. 58, has been modified, added to, and divided by several 

 authors, such as Desor, Cotteau, L. Agassiz, Wright, A. 

 Agassiz, and Lovdn, and contributions to the anatomy of the 

 species of great importance have come from the last two 

 naturalists. The recent forms have been, to a certain extent, 



