﻿246 



CLYPEOPYGUS 



characters : — The shell tapers behind, is not so elevated, has a flatter dorsal surface and 

 less prominent central ridge in the inter-ambulacrum ; the apical disc is more central, and 

 the contour indicates a flatter form with less inflated sides. 



Locality and Stratigrap/tical Position. — This new species was collected by the Rev. 

 T. Wiltshire, F.G.S., from the Lower Greensand (Neocomian) at Shanklin, Isle of 

 Wight. 



Genus — Clypeopygus, A. d'Orbigny, 1850. 



Nucleolites (pars), Agassi:, Besor, Cotteau. 

 Echinobrissus (pars), Be Loriol. 

 Catopygtjs (pars), Agassiz. 



Diagnosis. — Test oblong, more or less depressed, upper surface convex, under surface 

 concave, mouth-opening excentral, nearest the anterior border ; peristome surrounded by 

 five rosettes of buccal pores, and separated by five prominent lobes, oral aperture regular, 

 pentagonal, with equal sides and a prominent angle anteriorly. Vent small, situated in a 

 deep groove with perpendicular walls and well-defined outline, extending nearly half way 

 up the dorsal surface of the single inter-ambulacrum, ambulacra narrowly lanceolate, and 

 subpetaloidal ; the anterior and posterior pairs, especially the latter, long and flexuous. 

 The pores which compose the zones are sometimes unequal, the external series being 

 more or less elongated in a transverse direction ; apical disc small, excentral, and 

 composed of four perforated, and one imperforate genital plates, the right anterolateral 

 supporting the madreporiform body, which extends into the middle of the disc and forms 

 a prominence there; the five ocular plates are small and angled into the summits of 

 lanceolate ambulacra. The tubercles are very small and set closely together on the 

 upper surface (PI. LYI, fig. 1 /), and larger on the under surface (PI. LVI, fig. 3 g) ; 

 they are all encircled by areal depressions and separated by minute granules. 



This group was separated by M. A. d'Orbigny from Echinobrissus in consequence of the 

 following characters, which he observed to be constant in all the species : — The large central 

 polypiform madreporiform body; the mouth-opening surrounded by five rosettes of 

 pores, alternating with five well-developed buccal lobes; and the anal sinus circum- 

 scribed and contracted. 



The species are all special to the Cretaceous formations. M. d'Orbigny described 

 and figured six from the Neocomian and two from the Albian stages, and I now add 

 another form from the Neocomian of the Isle of Wight. 



