62 R. BULLEN NEWTON on 



ridges (as seen microscopically), which are continued over the surface of the 

 immediately surrounding region. The remaining sculpture consists of more or 

 less equi-distant, compressed, concentrically laminate structure, crossed by 

 numerous, close, microscopically fine, radial costae, which are irregular in their 

 descent to the ventral margin. The valve is thin (probably a young form), 

 rather longer than high, and is supplied with a narrowly oblong and horizontal 

 ligament compressedly triangulate, and basally wide at the ' resilium ' centre ; 

 there is present, also, a prominent semilunate adductor scar which is posteriorly 

 attenuated or produced above, whilst the margins exhibit some obscure 

 evidence of crenulations, especially on the anterior side. The valve shows a 

 much less elongate contour than characterises the true O. ludensis. 



DIMENSIONS. 



Length ... ... ... ... ... 25 millimetres. 



Height ... ... 30 



It would be premature to base the specific determination of an oyster on 

 only one valve, although the type of sculpture referred to is so unusual 

 among Ostreiform shells that if not O. ludensis it certainly belongs to a 

 closely related species. Deshayes described this shell from the Sables Moyens 

 of the Paris Basin, which belongs to the Bartonian Eocene. 



DISTRIBUTION. Eocene (Barton or Ludian Beds). 

 OCCURRENCE. Cutting No. i. 

 COLLECTOR. Mr. Kitson. 



Crassest rea Jugardi, sp. nov. 

 PLATE 6, fig. i ; PLATE 7, fig. i ; PLATE 8, fig. i. 



DESCRIPTION. Shell inequivalve, concavo-convex, oblong, thick, strong, 

 tapering above, margins crenulate near hinge, with slightly curved and more 

 or less parallel sides, height about twice the length. Lower valve interiorly 

 excavated, undulating, furnished with an elongate, triangular, tripartite, 

 frequently curved ligament region bearing equi-distant growth-lines with 

 intermittent finer lines crossed by innumerable microscopical perpendicular 

 striations ; the ' canal ' or central part of ligament area has a widened base 

 and is much excavated, lateral platforms depresso-convex with outer margins 

 composed of the closely arranged terminal laminations of shell structure > 



