198 POLYCYPHUS. 



the centre of the plates alone extending from the peristome to the disc ; the tubercles on 

 the ,sides and upper surface of the ambulacra and inter-ambulacra are nearly of a uniform 

 size, and regularly arranged in a series of horizontal and vertical rows (fig. 4/), so that 

 the tubercles are opposite each other, and do not alternate as in Magnotia. 



The poriferous zones are wide and straight (fig. 4 5, c) ; the pores are arranged in 

 oblique trigeminal ranks (fig. 4/) ; at the base they are more crowded (fig. 4 e), to fill up 

 the space between the ambulacral and inter-ambulacral areas. 



The base is flat (fig. 4 e) ; the large mouth opening is nearly pentagonal, and lies 

 in a concavity, surrounded by the larger tubercles which occupy this region (fig. 4 c) ; the 

 peristome is feebly notched (fig. 4 c), and very unequally lobed, the ambulacral being three 

 times the length of the inter-arabulacral lobes. 



The apical disc is small and prominent (fig. 4 h) ; the genital plates are all nearly of 

 the same size (fig. 4 d), and perforated near their apex ; the ocular plates are small, and 

 the eye-holes marginal ; the vent is transversely oblong (fig. 4 d), and the genital plates 

 form a prominent ring around it ; the spongy madreporiform body is rather elevated, and 

 a few microscopic granules adorn the surface of the plates. 



Affinities and differences. — In its general /(2;c2>5, this little lobed and nodulated urchin 

 resembles Magnotia Forbesii, but in the details of its structure it is very distinct from that 

 form ; thus its ambulacral areas and poriferous zones are wider, the median inter- 

 ambulacral sulcus is shallower and not so defined, the tubercles are larger and arranged 

 in a series of vertical and horizontal rows, and the pores are disposed in oblique trigeminal 

 ranks ; the test is likewise more hemispherical and inflated, and wants the marked sub- 

 pentagonal outline, the narrow furrowed zones, and deep median sulci which so well 

 characterise Magnotia Forbesii. 



Locality and Stratigrapldcal position. — ^This species is very rare in England. I have 

 collected one specimen from the Trigonia grit, Inferior Oolite, near Hampen ; Mr. Jones 

 found another near Birdlip, in the same rock ; the Rev. P. B. Brodie collected one specimen 

 from a bed of clay resting on the Stonesfield slate at Sevenhampton, associated with 

 Acrosalenia spinosa and Pecten varians ; Mr. Lycett obtained several from the Great Oolite 

 of Minchinhampton Common ; these are the only specimens known to me which have 

 been collected in Gloucestershire. Mr. William Buy found a beautiful specimen in the 

 Cornbrash near Sutton-Benger, Wilts, which is in my collection. He informs me that it 

 is the only example of this urchin he has found. It was associated with Acrosalenia 

 hcmicidaroides, Acrosalenia spinosa, and other Cornbrash fossils ; so that the range of this 

 species is from the upper ragstones of the Inferior Oolite through all the intermediate beds 

 into the Cornbrash, where it becomes extinct. 



On the Continent it is more abundant. It has been collected from the Great Oolite 

 of Langrune and Luc by Professor Deslongchamps and M. Tesson ; and from the Calcaire 

 a polypiers at Ranville by M. Michelin. I have to thank each of these gentlemen for the 



