162 PELTASTES 



of the sculpture of the disc ; the outer border of each ocular plate forms a crescent around 

 the summit of the ambulacra, and the terminal portions of the ovarial plates form an elegant 

 five-leafed petal extending down the middle of the inter-ambulacra ; the outer margin 

 of the disc is therefore very deeply incised between the ovarial and ocular plates, and 

 produces a structure which will be better understood by an examination of fig. 1 g, mag- 

 nified four diameters, than by any verbal description. The vent is large and the periprocte 

 bluntly diagonal, angular at the sides, and less convex before than behind (fig. 1 g) ; when 

 viewed in profile, as in fig. 1 a and d, the apical disc is conspicuously prominent, and the 

 elevated periprocte is seen to be very excentral and projected far backwards. 



Affinities and Differences. — This beautiful species in its general characters resembles 

 Salenia Austeni, Forbes ; but a careful comparison of the tests of both species discloses 

 important differences ; the ambulacra in P. Wiltshirei are narrower, with only two rows of 

 oblong marginal granules throughout, whilst S. Austeni has four rows in its wider 

 ambulacra. The inter-ambulacral areas in P. Wiltshirei are wider, and the primary 

 tubercles therein fewer and larger than in S. Austeni. The apical disc of P. Wiltshirei 

 is much larger ; the marginal incisions are deeper, the lines of sculpture wider, and the 

 periprocte is in the axis of the suranal plate. 



This species resembles P. JBunburyi, Forb., in the general structure of the test, and of 

 the apical disc ; the inter-ambulacral areas in P. Wiltshirei are wider, the tubercles are 

 larger and more regular, the apical disc covers a wider surface of the test than in P. 

 Bunburyi, and is deeply sculptured after a different pattern, both around the margin and 

 along the sutures of the plates. 



Locality and Slratigraphical Position. — This Peltastes is a very rare Urchin in the Red 

 Chalk of Hunstanton Cliff, Norfolk, where it was found by the Rev. T. Wiltshire, F.G.S., 

 who has contributed a valuable paper on this stratum to the ' Quarterly Journal of the 

 Geological Society,' 1 and from which I have made the following quotations, as the true 

 position of the Red Chalk is well defined in that communication. I am indebted to the 

 kindness of the Council of the Geological Society for the use of the annexed woodcut 

 illustrating the stratigraphy of this locality. 



Hunstanton Cliff "is marked by three parallel coloured bands, slightly inclined, and 

 cropping out in succession on the surface soil, of which bands the uppermost is white, the 

 next bright red, and the lowest yellow, each division being sharply defined, without any 

 intermingling of tints at the line of contact. . . . The highest stratum, the white, con- 

 sists of a hard calcareous substance, compact in texture, and much shattered and fissured, 

 originally deposited in such a manner that its materials were arranged in definite layers, 

 two of which (a b), those forming the base, are represented in the annexed section drawn 

 to scale. The first of these (a), in thickness about 2 feet 6 inches, is noticeable for the 

 presence of an enormous quantity of fragments of Inocerami dispersed throughout its 



' 'Quart. Journ. Geol. Soc.,' vol. xxv, p. 183, 1869. 



