336 ECIilNOBKISSUS 



valley (fig. 1 d). The surface of all the plates is covered with small, close-set, spiriigerous 

 tubercles, surrounded by circular areolas, and having the interspaces minutely granulated 

 (fig. \ e). At the base the tubercles are larger, their summits are perforated, and they 

 are surrounded by wider and deeper areolas (fig. 1 h). The diagram of the dorsal structure 

 (fig. 1 '/) shows the relative disposition of the plates in both the areas and poriferous zones, 

 and fig, 1 /?: is a correct figure of the Rev. A. W. Griesbach's unique and largest 

 specimen from the Cornbrash of Rushden. 



The apical disc (fig. 1 y) is composed of four perforated ovarial plates, and a small 

 imperforate ovarial. The right antero-lateral plate is the largest, and extends into the 

 centre of the disc ; it supports on its surface a prominent spongy madreporiform body. 

 The left antero-lateral and postero-lateral ovarials are about the same size ; the oviductal 

 holes in each are near the apex of the plates ; the single imperforate plate is much smaller 

 than the others. The five ocular plates. Math marginal eye-holes, are wedged in the angles 

 of the ovarials, and the surface of all the discal plates is granulated. Fig. 1 y represents 

 these discal elements in the most perfect development I have ever met with them in this 

 species, and it is, I believe, the first correct figure which has been given of the apical disc 

 of this common and well-known urchin. 



The base is more or less concave, most so in the pyramidal varieties (fig. 1 b) ; the 

 ambulacral areas radiate in depressed furrows from the margin of the mouth-opening, 

 becoming shallower and wider as they approach the border. The poriferous zones are 

 more apparent near the peristome, and the pores lie close together in oblique pairs. The 

 mouth-opening is excentrical, being situated in a deep depression nearer the anterior than 

 the posterior border. The tubercles at the base are larger and set wider apart than those 

 on the dorsal surface ; their summits are likewise perforated, and their bosses surrounded 

 by wider and deeper areolas (fig. 1 h), the intermediate space being filled with larger 

 granules. 



Affinities and differences. — This species resembles very much E. scutatus, Lamk., and 

 E. dimidiatus, Phil. ; it is distinguished from these forms by the length of the anal 

 valley, which extends from the disc to the margin, whilst in E. scutatus, Lamk., and 

 E. dimidiatus, Phil., there is an undepressed portion of test between the disc and the 

 commenceujent of the valley. The posterior lobes are likewise more tapering and less 

 tumid than in the Coral Rag species. E. clunicularis is distinguished from E. orbicularis, 

 Phil., by its sub-quadrate shape, by its sides increasing in diameter towards the posterior 

 part, and by its posterior bilobed border. The same group of characters serve to dis- 

 tinguish it from E. Woodwardii, Wright, a species remarkable for its tumid sides and long 

 narrow anal valley. 



Localiti/ and Stratip'apJdcal position. — This urchin makes its first appearance in the 

 Clypeus Plottii bed of the Inferior Oolite, in the zone of Ammonites Farkinsoni. The 



