148 THE FOSSIL ECHINOIDEA 



Illustrations of the Species in Plate XXVII. 



Fig. 4. Abactinal view of the test : natural size. 



5. Actinal view of the test: natural size. 



6. Longitudinal profile of the test : natural size. 



4. Amblyptgus latus, Duncan & Sladen. Plate XXVII, Figs. 7-9. 



Test depressed, marginal contour subcircular, dilated transversely, the greatest 

 diameter being situated a little behind the antero-lateral ambulacra. The rounding of 

 the posterior portion of the marginal outline' is somewhat flattened, and that of the 

 anterior part more regularly circular. The height of the test is two fifths of the 

 breadth, and proportional to the length as 0'41 : 1 ; and the dorsal surface is low but 

 regularly convex, the margins being thick and tumid. The anterior slope of the 

 longitudinal profile is more rapid than the posterior portion, and the test, as a whole, 

 is rather more bombous along the lines of the posterior ambulacra than elsewhere. 

 The transverse profile of the dorsal surface shows a regular convexity of wide curvature. 

 The actinal surface is concave, the peristome being well sunken, and the surrounding 

 portions of the test bombous, the convex curve merging without interruption with that 

 of the inflated margin. 



The apical disk is excentric in front, being distant from the posterior extremity 

 To'(S of *h6 entire length of the test. There are four generative pores, which are 

 rather small, and the anterior are slightly nearer together than the posterior pair. 

 One of the posterior pores is long and slit-like in the specimen under notice. The 

 ocular plates are very small. The central madreporiform body is ornamented with a 

 few small and rather widely-spaced granules. 



Tlie ambulacra are flush with the surface of the test and moderately wide ; and 

 the petaloid portion dies out before the actual margin is reached, where the dorsal 

 surface commences the sharper curve of that part of the test. The ambulacra are 

 equal, and the widest portion is situated somewhat nearer the apex than in the pre- 

 ceding species, and corresponds almost exactly with the widest part of the poriferous 

 zone ; at this place the width of the poriferous zone is exactly one half that of 

 the interporiferous area. The interporiferous area attains its greatest width at the 

 margin, where it is more tha.n three times the width of the broadest portion of the 

 poriferous zone. The outline of the petal is lanceolate ; and the poriferous zones, after 

 attaining their greatest width, taper off' somewhat rapidly in breadth to the extremity 

 of the petaloid portion of the zone. The conjugate pores are united by a well-defined 

 groove, and the intervening septa are broad and ornamented by a single line of com- 

 paratively large granules. The extrapetalous portion of the zone consists of pairs of 

 pores throughout, and is flush with the actinal surface of the test, no trace of any 

 groove being present. The details of the structure of the ambulacra are similar to 

 those described in the preceding species. 



The ornamentation of the specimen has, unfortunately, been very badly preserved. 



