ISO SALENIA 



Bimensions. — Specimen a. Altitude, four lines ; latitude, five lines. 



„ b. Altitude, four and a half lines ; latitude, six and a half lines. 



Description. — This beautiful species was first noticed by M. I'Abbe Sorignet, in his 

 description of ' I'Oursins de I'Eure,' and referred by him to Ili/posalenia heliophora from 

 the Upper Chalk (Danian) of Ciply, which M. Desor' described as " distinguished by its 

 very much ornamented disc, each ovarial and ocular plate being the centre of a system of 

 fine ridges, that radiate in all directions." This species was not figured by Sorignet; and 

 I have not yet seen a French specimen to compare with our Urchin from the lower 

 white gritty Chalk of Dover, where it has hitherto only been found. 



The test is small and circular, the upper surface convex, the lower flat, and the sides 

 rounded and moderately inflated (PL XLI, fig. 2c; PI. XLIII, fig. 1 d). The ambulacral 

 areas are narrow, straight, or slightly flexed, with two niai-ginal rows of round prominent 

 granules, twelve to thirteen in each ; those near the base are large and raammillated 

 (PI. XLI, fig. 1 e) ; those at the ambitus smaller, and on the upper part very small and 

 closely placed together ; the intermediate space being filled with an unequal microscopic 

 granulation, which extends horizontally between the marginal granules. 



The poriferous zones are narrow, the pores unigeminal, and set in oblique pairs, 

 separated from each other by a small granuliform elevation of the septum ; there are 

 about eight pairs of holes opposite one of the large inter-ambulacral plates (PI. XLI, 

 fig. 2/; PI. XLIII, fig. 1 li, in which I have given accurate figures of this part of the 

 test, magnified six times). 



The inter-ambulacral areas are wide (PI. XLI, fig. 2 d), and covered over in their 

 upper third by a lateral extension of the ovarial plates ; there are three or four tubercles in 

 each row, which rise a little above the ambitus; only one or two of these tubercles in 

 each series are well developed, surrounded by a circular areola, and having a large boss 

 and prominent mammillon (PI. XLIII, fig. 1 // ; PI. XLI, fig. 2/). The miliary zone is 

 narrow, and its granules unequal in size and structure ; the larger are distinctly mammil- 

 lated, and disposed in a regular crescentic form around the areolae ; where the latter abut 

 against the poriferous zones the granules are absent (fig. 1 h, fig. 1 g) ; the other granules 

 are small and irregularly disposed, filling up the space with a fine granulation (fig. 1 h). 



The mouth-opening is very small (PI. XLI, fig. 2 (5 ; PI. XLIII, fig. 1 c), in excess of 

 one third the diameter of the test ; the peristome is divided into ten equal lobes by well- 

 marked incisions. 



The apical disc is very large and pentagonal, occupying a great part of the upper 

 surface (PI. XLIII, fig. 1 b, d, e). It is convex above, and so thin and closely adherent to 

 the shell at the borders that it appears to blend witli the plates of the test ; the ovarial 

 plates are large, and of an irregular form ; their surface is sculptured with small unequal 

 punctuated lines, which appear to radiate outwards from the oviductal holes situate near 



' 'Synopsis des ficliinides fossiles,' p. 148. 



