﻿FROM THE LOWER GREENSAND. 



245 



Catopygus Vectensis, Wright, nov. sp. PI. LV, fig. 1 a — d. 



Diagnosis. — Test oblong, contracted posteriorly ; dorsal surface flat and convex, 

 elevated towards the narrow posterior border; sides inflated, base concave.; ambulacra 

 narrow, lanceolate, dorsal, subpetaloid, and open below ; inter-ambulacra wide, single 

 inter-ambulacrum narrow, slightly elevated ; posterior border truncated ; vent oblong, 

 in the upper third; an obtuse elevation of the dorsal portion, bifurcating at the 

 periprocte, sends down a carina on each side of the vent, which extends to the 

 margin. Apical disc nearly central, four perforated genital plates ; madreporiform body 

 small, central. 



Dimensions. — Length one inch ; breadth eight tenths of an inch ; height unknown. 



Description. — This species has much resemblance to certain varieties of Catopygus 

 columbarius but a careful comparison between it and the most allied forms of that 

 species shows that Catopygus Vectensis possesses distinct characters of its own. It is, I 

 believe, the oldest form of the genus Catopygus at present known. The outline of the test 

 is nearly a regular oblong, rather more contracted posteriorly (PI. LV, fig. 1 a, b). It is 

 moderately elevated and a little higher at the posterior border (fig 1 c) ; the sides are 

 inflated (fig. 1 d), and the base is concave; this portion of the test is partially covered 

 by closely adherent matrix in the best specimen, and broken in the other, so I must 

 speak with reservation regarding the specific characters of this region. The ambulacral 

 areas are narrowly lanceolate (fig. 1 b, d), and the long subpetaloid poriferous zones extend 

 over the dorsal surface, a character which is very well drawn in figs. 1 a, b, c, d ; the 

 traject line of the pores is indicated by the sutures in which they are placed, but the 

 pores themselves cannot be satisfactorily made out in consequence of the imperfect 

 preservation of the areal plates. 



The inter-ambulacral areas are built of long plates ; those on the upper surface had 

 very small tubercles which appear to have been more developed at the base ; the posterior 

 single inter-ambulacrum has an elevated ridge on the mesial line which extends to the 

 upper border of the vent (fig. 1 o), and then divides into two branches (fig. 1 d) ; which 

 descend to the border, the whole forming a kind of miniature Gothic arch, having 

 the oblong vent in its upper third (fig. 1 c and d). 



The apical disc is nearly central (fig. 1 b), and lower than the vertex (fig. 1 (?) ; it is 

 small, has four genital holes drilled around a small central button-shaped madreporiform 

 tubercle. 



The mouth-opening is excentral and anterior ; it is too much concealed by hard rock 

 to be exposed without risking the fracture of the shell, so the anatomy of the peristome 

 cannot be made out. 



Affinities and Differences. — This species differs from C. columbarius in the following 



