Br. F. A. Bather — Eocene Echinoids from Sokoto. 301 



after that none are distinguishable. Pore-pairs, not conjugate, 

 slightly oblique, the outer pores being adapical and depressed in 

 a slight peripodium. 



The paired ambulacra are relatively deeper and wider in B than 

 in A, suggesting that B was female and A male. They are almost 

 straight, subpetaloid, and asymmetrical, the anterior half of II and 

 IV, the posterior half of I and V, becoming the narrower towards 

 the apex. II and IV subtend 110°. Length of petal, in A, 13-5 mm. 

 (distance to margin along curve being 19'5 mm.), in B, 11-3 mm. 

 (distance to margin, 14-8 mm.). Greatest width in A, 3"8 mm. at 

 about 4 mm. from distal end of petal ; in B, 3-5 mm. at about 

 5-3 mm. from end. Width at distal end of petal, 2*3 ram. in A, 

 2'1 mm. in B. Deepest part of petal at 6 mm. from apical system. 

 Poriferous areas broad, extending almost to outer margin of ambu- 

 lacrum, especially on posterior side. Pores conjugate ; elongate, 

 except 2 adapical pairs in the posterior half, 7 adapical pairs in the 

 anterior half, and the extreme distal pair, all of which are circular. 

 Outer pore of each pair slightly more distal and twice length of 

 inner pore. Height of ambulacrals, "6 mm. in A, '5 mm. in B. In 

 A the pores lie in the distal half of each plate, and the proximal hal f 

 is marked with a line of six miliaries ; B differs in having the pores 

 nearer the middle of the plate. Each series contains 28 pore-pairs 

 in A, 26 to 27 in B. Interporiferous area narrow (-75 mm. in A) 

 and slightly grooved. (PL XI, Fig. 10.) 



Ambulacra I and V subtend 60°. Length of petal, in A, 10 mm.,^ 

 in B, 8*3 mm. Greatest width at about half the length, 3'2 mm. 

 in A, 3-4 mm. in B. Width at distal end of petal, 2-2 mm. Eacli 

 series contains 21 pore-pairs in A, and 19 in B ; of these the 3- 

 proximal in both specimens, the 3 distal in B, and the extreme distal 

 in A are circular. In all other respects these ambulacra resemble 

 II and IV. 



Interradials. — As previously stated, B affords evidence of normal 

 heteronomy in 1. The number of petal-ambulacrals abutting on an 

 interambulacral of 1 in A is 6. The small labrum is succeeded by 

 two large sternals, which swell up to the median line ; at the end of 

 the sternum, about 15-5 mm. from the peristome in A, the inter- 

 radius curves gently round to the margin, where it meets the 

 posterior truncation. These structures are more clearly shown in 

 the Tamaske specimens (PL XI, Fig. 12). 



Peristome. — In A the transverse diameter is 3-2 mm., the sagittal, 

 1-6 mm. The anterior sulcus is continued right up to its anterior 

 margin, which is 7-6 ram. from the anterior vertical plane. Anteriorly 

 and laterally is a slightly raised rounded rim. Posteriorly, the 

 labrum projects over the opening, and is raised about 1*4 mm. above 

 the level of the anterior lip. (Of. specimen I ; PL XI, Fig. 12.) 



Periproct. — Vertically elongate, broadly lanceolate, more pointed 

 above, situate at upper end of posterior truncation, at about 11*5 mm. 

 above base-plane in A, with length 4-8 mm., and width 3-3 mm. 



Ornament. — Primary tubercles best preserved on the sides of the 

 anterior groove, where they are larger, and on its floor, where they 



