Dr. F. A. Bather — Eocene Echinoids from Sokoto. 295 



and all the space within the gonopores is filled with hydropores ; 

 the madrepoiite does not, however, extend backwards between the 

 posterior oculars. (PL XI, Fig. 2.) 



Ambulacra. — At the ambitus and on the tumid margin of the 

 actinal surface the whole ambulacral area is slightly raised ; within 

 the petals the raising is almost confined to the interporiferous area, 

 the poriferous areas being slightly depressed along their outer 

 borders. The petals do not reach the ambitus, the posterior pair 

 being the most remote from it. Angle included by rays II and IV, 

 135° ; by rays I and V, 60°. The petals widen equably to near 

 their ends, then close in slightly ; the actual measurements are : — 



III. II & IV. I & V. 



Length of petal ... 207 mm. 20-0-21-6 mm. 24-0-25-0 mm. 



Greatest -width ... 6"9 mm. S'O- 7'5 mm. 8-4- 8'0 mm. 



Width at distal end 5-0 mm. 4-3 mm. 5-3 mm. 



Structure of petals : — In all lateral petals the posterior poriferous 

 area curves more than the anterior (PL XI, Figs. 4 and 5). In 

 ray IV, at the widest part of the petal, the width of the inter- 

 poriferous area is 3-8 mm., while that of the poriferous area is 

 2'1 mm. ; the widths of both diminish slightly towards the apex and 

 more slightly towards their distal ends. The inner pores of an 

 area are almost circular, the outer pores pyriform on the surface but 

 becoming more circular deeper down, as is seen when the surface 

 has been worn. This appearance is connected with the distinct 

 conjugation of the pores. In the interporiferous area the sutures 

 between the ambulacrals are almost at right angles to the perradius, 

 with a tendency to slope adactinally from it. In the poriferous 

 areas the adactinal slope of the suture is conspicuous, the angle 

 contained by the two regions of the suture being 150°. Number of 

 pore-pairs in petals : III, circa 48 ; II and IV, circa 51 ; I and V, 

 circa 60. But tliere are a few slight irregularities : thus, in the 

 anterior poriferous area of ray IV, reckoning from the distal end of 

 the petal, the outer pores are missing from sutures 1, 3, 4, 6, 7, 8, 

 the inner pores remaining normal, except 3 and 4, which are 

 diminished; outer pore 5 is larger than usual (PL XI, Fig. 4). 

 Occasional atrophy or suppression of a pore occurs in the other rays. 



From the contracted ends of the petals the ambulacra widen again 

 towards the ambitus, and then lessen in width towards the peristome, 

 widening slightly just before they reach it. The series of double 

 pores of the petals changes very rapidly, if not quite abruptly, into 

 a series of minute single pores which appears to continue the inner 

 row of the double pores. It passes over the ambitus on to the 

 actinal surface of the test ; as it approaches the peristome the pores 

 increase in size, and at the oral end of the ambulacrum appear to be 

 some half-dozen supplementary pores on each side, forming a rudi- 

 mentary phyllode. This is more clearly seen in B (Text-fig. 4). 

 but the structure in A seems to have been similar. 



Interradials. — In the upper part of the abactinal surface, the 

 sutures between these plates are straight ; in the lower part the 

 sutures have a downward bend in the middle. The number of 



