from the Lias and Oolites. 35 



depth of the poriferous avenues being greater than the sulcus 

 which divides the interambulacra. 



The mouth is large and decagonal, and lies in a concave 

 depression in the base, surrounded by the larger tubercles 

 which occupy this region of the test. The ovarial plates are 

 small, and form a rather prominent ring around the anal open- 

 ing ; the eye-plates are small, but in some of the foreign indivi- 

 duals now before me the eye-holes aue very distinct. 



Affinities and differences. This Urchin resembles Arbacia 

 Forbesii, but may be distinguished from that species by having 

 the ambulacral areas proportionately wider, the tubercles larger 

 and opposite to each other, and the poriferous avenues having 

 the pedal holes in triple oblique pairs ; it belongs moreover to a 

 newer rock of the Oolitic series. 



Locality and stratigraphical range. We know only one English 

 specimen of this species, which was found in the Cornbrash by 

 Mr. Buy near Sutton Benger, Wilts ; on the continent it occurs 

 in the Baireuthian Jurakalke, where it was found by Count Miin- 

 ster. It has been collected from the Great Oolite of Langrune 

 by Prof. Deslongchamps and M. Tesson, and from the Calcaire i\ 

 polypiers at Ranville by M. Michelin. We beg to record to each 

 of these gentlemen our best thanks for the beautiful series of 

 type specimens of this Urchin with which they have so liberally 

 supplied us. 



History. Figured and described for the first time by Gold- 

 fuss. We are not aware that any detailed description of the spe- 

 cies has been given before, with the exception of the very brief one 

 contained in the f Petrefacta Germanise/ 



Polycyphus Deslongchampsii, Wright. PL II. fig. 4, a-e. 



Test hemispherical, circumference circular; ambulacral areas 

 with two rows of larger and two rows of smaller tubercles ; 

 interambulacral areas with two rows of larger and several rows 

 of smaller tubercles ; the small tubercles in both areas often 

 degenerating into mere granulations; basal tubercles large 

 and prominent. 



Height /jjths of an inch, transverse diameter ths of an inch. 



Description. Amongst the many beautiful forms of Urchin 

 structure, this pretty little species will bear comparison for neat- 

 ness and symmetry with any of the family to which it belongs. 

 We found the first specimen about eighteen months ago, and since 

 then have added an interesting series to our collection. It must 

 be a rare form, as only two or three specimens have been obtained 

 besides those collected by ourselves. The ambulacral areas are 

 one half the width of the interambulacral, and have one row of 



D2 



