FROM THE MEDIAL CHALK. 225 



other specimens exhibiting the jaws have been discovered. The teeth are small, smooth, 

 white, lanceolate, triangular, each consisting of a concave lamina, terminating below in 

 the dental point, and strengthened by a prominent ridge behind (fig. 6). 



The base is flat, and both areas are covered with much larger tubercles than those 

 developed on the dorsal surface ; they are arranged in irregular concentric rows around the 

 peristome ; the single inter-ambulacrum is elongated posteriorly, and more tumid towards 

 the border, which is sometimes rostrated and recurved (PI. XLIX, fig. 2 and fig. 4, and 

 PI. L, fig. 1 and fig. 2). In this portion the vent opens ; this aperture is one third 

 larger than the mouth, and broadly elliptical in a longitudinal direction ; its margins are 

 thick and elevated, and appear to have supported an anal membrane. The vent is 

 marginal in a majority of specimens, and is rarely seen above the border ; most frequently 

 it cuts that angle obliquely (PI. L, figs. 1 and 2). 



The apical disc (PL L, fig. 1 e) is quadrangular, and formed of four perforate 

 and one small imperforate ovarial plates ; the right antero- lateral is the largest, and 

 extends into the centre of the disc, its surface supports the madreporiform body ; the five 

 ocular plates are small cordate elements, closely wedged in the angle between the ovarials. 



Jffinities and Differences. — This typical species difiers from its congeners in its form, 

 which is always conical or pyramidal ; the base is flat and sub-pentangular, and the single 

 inter-ambulacrum is posteally produced, being somewhat tumid and recurved. These 

 characters readily distinguish it from E. castanea. The straight, slightly inclined sides, 

 the acute ambital angle, and flat base, form a good diagnosis between it and E. subrotimdus, 

 which lias convex sides, a rounded ambital border, narrow base, and small inter- 

 ambulacrum ; the conical form, small tubercles, and large vent distinguish it from 

 E. abbreviatiis. 



LocaUty and Sir atigraphical Position. — This species is found in abundance in the 

 white Medial Clialk of the English Cretaceous districts. It is very Common in the south ; 

 fine specimens are obtained at Gravesend and other localities in Kent, and at SwafF- 

 ham, in Norfolk. Specimens showing the dentiferous jaws are in the collections of Mr. 

 Stokes, Dr. Bowerbank, and my kind friend the Rev. T. Wiltshire, F.G.S. ; to whom I 

 am indebted for the figured specimen. 



Foreign Localities. — In France, according to M. Cotteau, it is found in I'fitage 

 Senonien, at Meudon, near Paris, near Sens, Villeneuve-le-Roi, and Charny, Yonne; 

 Beauvais and Roquemont, Oise; Chartres, Eure-et-Loire ; Vernonnet and Pinterville, 

 Eure ; Bains-de-Rennes, Aude ; the environs of Aix-la-Chapelle, and in the Island of 

 Ruegen. 



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