320 Dr. T. Wright on new Species of Echinodermata 



lanceolate; posterior lobes short and truncated; base flat; 

 antero-interambulacra and postero-interambulacra slightly 

 swollen at their base; the single ambulacrum scarcely pro- 

 duced ; mouth-opening pentagonal, situated anteriorly ; apical 

 disc small and nearly central. 



Height y^ths of an inch, antero-posterior diameter 1 inch and 

 J^th, transverse diameter 1 inch and y%ths ; the larger speci- 

 mens are so much deformed by pressure that their proportional 

 dimensions cannot be accurately given. 



Description. — Some individuals of this species were formerly 

 considered by ns to be only varieties of Nucleolites orbicularis, 

 Phil., but a better knowledge of the structure of this Urchin, 

 derived from the study of a series which we collected last summer 

 and have carefully compared with good typical examples of A^. or- 

 bicularis, leaves no doubt about the distinctness of N. Woodwardii 

 from that Cornbrash form. The test is thin and not often suffi- 

 ciently well preserved for determining the species; the one which 

 we have figured is a small but a very perfect specimen, it has a 

 subquadrate outline and is joth of an inch broader than it is in 

 the antero-posterior diameter; it is slightly narrower anteriorly 

 than posteriorly, and (which is more apparent when it rests upon 

 its dorsal surface) the posterior margin is seen to be broadly 

 truncated; the sides are tumid, sometimes irregularly so, and 

 the test is higher across the apices of the postero-lateral ambu- 

 lacra than at any other point ; the tumidity of the sides produces 

 a greater flatness of the dorsal surface than we observe in any 

 other of the small Nucleolites of the Oolitic rocks ; the ambu- 

 lacral areas are nearly all of the same width, they have a narrow 

 graceful lanceolate form, from the mouth to about midway 

 between the margin and the apical disc, they are nearly of equal 

 width; at this point the pores gradually change their form, and are 

 slightly separated apart for a short distance, and begin again to 

 converge as they approach the disc ; the internal row are circular, 

 the external in the form of oblique slits, the widest part of which 

 is outwards, the circles are formed by notches in the upper and 

 under sides of the small ambulacral plates, and the oblique slits 

 by uncalcified portions of the margins of the same plates ; from 

 the termination of the petaloid portion of the ambulacral areas 

 to the mouth, the pores are small and set wider apart, whilst 

 the diameter of the areas remains about the same; near the 

 mouth-opening they are again more closely crowded together, 

 and terminate in arches the convexity of which look towards 

 that aperture ; the interambulacral areas are of unequal width ; 

 the anterior pair are the narrowest, the posterior pair are wider 

 than the anterior, and the single interambulacrum is the widest; 



