56 THE FOSSIL ECHINOIDEA 



Fig. 5. Another specimen ; the test, from above. 



6. Part of an ambulacrum : magnified. 



7. The peristome : magnified. 



8. The peristome : more highly magnified. 

 '' 9. The longitudinal outline of the test. 



Plate XIV. 

 Fig. 1. The rudimentary phyllode : magnified. 



2. Plesiolampas pe^longa, sp. nov. Plate XIV, Figs. 2, 3. 



The test is elongate, the length in proportion to the breadth as 7 : 5, subdepressed 

 and convex above, very tumid at the sides and in front, subrostrate posteriorly. Mar- 

 ginal contour elliptical, widest posteriorly opposite the extremities of the posterior 

 petals, and then contracting somewhat rapidly to the posterior point ; anterior to the 

 widest part the outline is almost paraboloid. Actinal surface very tumid, with the 

 peristome deeply impressed and the tumidity of the test slightly less in the posterior 

 median line than elsewhere. The longitudinal profile shows the abactinal surface of 

 the test to be very level, passing down with rather a rapid but well-rounded curve 

 along the posterior rostration. The transverse profile presents rather a flatly convex 

 outline, tumid at the sides, and bending round onto the actinal surface with an unin- 

 terrupted curve. 



The apical system is small and excentric in front, its distance from the anterior 

 extremity being little more than one third of the length of the test. There are four 

 generative pores, the posterior pair larger and slightly wider apart than the anterior 

 pair, and with two rather conspicuous small tubercles, similar to those which ornament 

 the test, standing in a line drawn between the posterior pores. The madreporic body 

 occupies the central space, and is prominently convex. 



Ambulacra small, distinctly petaloid, converging towards their outward extremities ; 

 the antero-lateral petals terminating at a distance from the margin equal to one third 

 of the length of the petal, whilst the posterior pair terminate at fully their own length 

 distance from the margin. The petals of the paired ambulacra are of equal width, but 

 the posterior pair are slightly longer than the anterior. The posterior poriferous zone 

 of the antero-lateral ambulacra is somewhat longer by 2 or 3 pairs of pores, and more 

 curved than the anterior zone ; in the posterior petals, the curvature of the zones is 

 equal, and their length does not diff'er by more than one pair of pores. The odd ambu- 

 lacrum is covered by matrix. The anterior pair form a wide angle with one another, 

 and the posterior pair a much smaller one. 



The poriferous zones are narrow and slightly broadest at the middle of the zone, 

 their width here, however, being less than one half the breadth of the interporiferous 

 area. The inner pores are round, and the outer slightly elongate transversely ; and 

 they are united by a faint conjunctive furrow, the costal ridges that separate the pairs 

 of pores being ornamented with a single line of minute uniform granules, five or six in 

 number at the broadest part of the zone. In the antero-lateral ambulacra there are 29 



