PROM THE UPPER GREENSAND. 251 



compressed, dorsal surface convex ; ambulacra lanceolate, subpetaloidal ; apical disc 

 excentral and forwards ; vertex central ; anal sulcus short, deep, and subtriangular ; base 

 concave ; mouth-opening pentagonal, slightly excentral, and forwards. 



dimensions. — Antero-posterior diameter half an inch ; height three tentlis of an inch. 



Description.- — -The test is oval and depressed, obtusely rounded before, a little 

 angular, subrostrated, and sloped out behind, and the greatest diameter is at the pos- 

 terior third. The upper surface is convex ; the longitudinal profile shows it to be rounded 

 and depressed at both extremities, with a slight excentral elevation nearer the anterior 

 than the posterior border. The ambulacra are long, lanceolate, and subpetaloidal on the 

 dorsum, narrower at the ambitus, and enlarged in the base ; the poriferous zones have the 

 pores unequal, and a little apart above where they form the petals ; they are close together 

 and microscopic at the ambitus, and are larger and more numerous near the mouth, where 

 they form a pentagonal star around the peristome. The anal sulcus occupies the lower 

 fourth of the single inter-ambulacrum ; it is short, deep, and triangular, and its two 

 lateral walls form prominent carinaj, the sulcus making an excavation in the posterior 

 border ; the vent is oval and opens at the summit of the valley. 



The apical disc is small, quadrate, with four perforated genital pores ; it is slightly 

 excentral and placed a little forwards, and forms the vertex of the test. 



The base is very concave, always near the mouth, and greatly undulated at the sides, 

 the single inter-ambulacrum being slightly subrostrated and recurved. 



The mouth-opening is excentral, the peristome pentagonal, with one angle directed 

 forwards, and the pores increase in size and number in the ten zones around this 

 aperture. 



The scrobiculated tubercles closely cover all the upper surface ; beneath they are larger 

 and not so numerous. 



Affinities and Differences. — This species, which is very rare in England, was said by 

 the late Professor A. d'Orbigny to resemble E. Bour(juigncdi, but to be distinguished 

 from it by having the test much more depressed, subrostrated behind, compressed at the 

 sides, humped at the vertex, and more concave and undidated on the under surface. 



Locality and Stratiyraphical Position. — According to the late Professor Porbes, who 

 first separated the species from E. lacunosus, and gave only an imperfect diagnosis without 

 any figure of the same, this Urchin is found in the Upper Greensand of Warminster and 

 Blackdown, and the type was detected in Professor Pennant's collection. On the Continent 

 it was collected by the late Vicomte d'Archiac from " I'Etage Cenomanien" at Brunswick. 

 Unfortunately the figure of this species was not drawn by my late lamented friend 

 Mr. Bone, as he was waiting to procure a good specimen to draw, and had not obtained 

 one when it was required. 



