Dr. T. Wright on the Cidarida? of the Oolites. 173 



with about ten rows of tubercles, about the same size as those of 

 the ambolacralj and like them set distinct from each other, which 

 gives the surface of the test a nodulated air ; a slight furrow passes 

 down the centre of the interambulacral arese, dividing them into 

 two parts ; the rows of tubercles diminish in number at the apex 

 and base of the area-, they are larger and more fully developed, 

 however, in the latter region; the apical disc is small, ring- 

 formed, and prominent; the poriferous avenues are deep and 

 strongly defined, the pores are arranged in simple pairs above, 

 but they form double ranges which fill up the wide space at the 

 basis of the area? ; the base is concave, the mouth is large and 

 pei it agonal like the former species, the notches are closely ap- 

 proximated at the bases of the interambulacra, and the marginal 

 arch over the ambulacra is straight and wide ; the tubercles dis- 

 posed at the bases of both area? are larger and more fully developed 

 than those occupying the sides. 



Affinities and differences. — The size of the tubercles and their 

 diminished numbers when compared with A. Forbesii serve as a 

 sufficient diagnosis whereby A. nodulosa may be distinguished 

 from the former Urchin; the slight median furrow down the centre 

 of the interambulacral arese is very different from the deep line se- 

 parating the area? in A. Forbesii into two equal nearly conical lobes. 



Locality and stratigraphical range. — This species was collected 

 by my friend the Rev. P. B. Brodie from the bed of clay resting 

 on the Stonesfield slate at Sevenhampton Common, along with 

 Acrosalenia spinosa and Pecten varians ; this bed occupies the same 

 relative position in other parts of Gloucestershire, and is probably 

 the basal clay band on which the shelly freestone beds of the 

 Great Oolite rest. I only know the solitary specimen before 

 me; in Germany, Count Minister found it in the Jurakalk of 

 Haireuth. 



History. — First figured and described as an Echinus by Gold- 

 fuss. I am not aware of its having been noticed before as a 

 British fossil. 



My thanks are especially due to Mr. W. H. Baily for the pains 

 he has taken with the beautiful figures which accompany this 

 paper, the original specimens of which are in my cabinet. 



