200 POLYCYPHUS. 



in pairs (fig. 5 c, d), those on the right alternating with those on the left side of the 

 area. 



The inter-ambulacral areas are twice the width of the ambulacral (fig. 5 6, d) ; a single 

 row of larger tubercles, about sixteen in each row, is placed in the centre of each of the two 

 columns of plates (fig. 5/) ; and numerous smaller tubercles, degenerating into granules, 

 occupy the rest of their surface (fig. 5/) ; a second row of tubercles extends from the base 

 to the circumference, where it terminates (fig. 5 c, d) ; the tubercles at the base of the 

 inter-ambulacra are about the size of those occupying the same region in the inter-ambu- 

 lacra ; there are twelve of these larger tubercles in each area, so that the base (fig. 5 c) has 

 a much more granulated appearance than the upper surface of the test (fig. 5 <5) ; as 

 the median sulcus in the centre of the inter-ambulacra is sharply defined, and the pori- 

 ferous zones are much sunk, the surface of the test is thereby nearly equally divided into 

 fifteen lobes. 



The poriferous zones lie in considerable depressions (fig. 5, d) ; the pores are very 

 indistinct, and arranged in oblique trigeminal ranks ; between each rank a small tubercle 

 is developed, which adds to the granulated aspect of this region, and renders the situation 

 of the pores still more difficult to trace (fig. 5/). 



The apical disc is small and prominent (fig. 5 a, b), the genital plates are nearly of 

 the same size (fig. 5 e), the spongy madreporiform body is small, and the oviductal holes 

 are pierced near the margin ; the ocular plates are small and heart-shaped, and the eye- 

 holes are distinctly marginal ; the vent is small, and transversely oblong. 



The base is flat (fig. 5 d), and remarkable for the much greater size of the tubercles 

 in this region than on the upper surface ; the mouth opening is one half the diameter of 

 the test, and the peristome is divided by feeble notches into ten unequal lobes (fig. 5 c.) 



Affinities and differences. — In its general fades, this species resembles Polycyphas 

 Normannus, but is readily distinguished from it by the marginal tubercles on the ambu- 

 lacra, the two central rows of larger tubercles on the inter-ambulacra, and the smaller 

 tubercles crowded around their base (fig. 5 f) ; by the row of tubercles between the 

 trigeminal ranks of pores, the comparatively small number of tubercles in the inter-am- 

 bulacra, and the greater size of the central rows. The tubercles at the base are likewise 

 much larger in Polycyphus Deslonychampsii. 



Locality and Stratiyraphical position. — I collected this urchin in the Pea-grit at 

 Crickley Hill, with Diadema depressum and Acrosalenia Lycettii. Mr. Gibbs, of the 

 Geological Survey, found a few specimens in the same rock and locality. 



I have dedicated this species to Professor Deslongchamps, of Caen, to whom palaeon- 

 tologists are indebted for many valuable memoirs on the Oolitic fauna, published in the 

 ' Memoires de la Societe Linneenne de Norniandie.' 



