232 FOSSIL SHELLS OF THE CRAG. 



from the coralline crag are sufficiently abundant ; those from 

 the red crag occur but rarely. 



The two figures referred to T consider to be of the same 

 species ; but must leave it for further observation to confirm 

 or refute this opinion. 



Area lactanea, Nob. PI. xiii. fig. 3. 



Shell transverse, decussated, anterior side subangulated, beaks approxi- 

 mate, margin entire. Longitudinal diameter, f ; transverse diameter f 

 of an inch. 



Red crag, Walton, Essex. Coralline crag, Sutton. 



This shell differs from Area lactea in being rather more in- 

 equilateral, and in being less angular at its anterior margin : 

 the ligamental area is also so much smaller as, in my opinion, 

 to render its separation from that species necessary. The 

 rays are numerous, and decussated by lines of growth ; the 

 teeth in the centre of the hinge-line are vertical, but they be- 

 come gradually inclined towards its extremities. Specimens 

 fi'om the red crag are often much distorted, like the recent 

 shell, so as to be nearly equilateral and scarcely transverse ; 

 but the anterior side always preserves a more rounded form 

 than any of the recent specimens that I have seen. There is 

 a small sinus in the basal margin. One antique specimen 

 from the red crag measures an inch in its transverse diameter. 



Area raridentata^ Nob. PI. xiii. ^^. 4. 



Shell subrhomboidal, tumid, externally rayed, teeth much inclined, mar- 

 gin crenulated. Longitudinal diam. ^; transverse diam. gg of an inch. 



Coralline crag, Sutton. 



An abundant species. The teeth in this shell are similar 

 in their arrangement to those of Cueullaa, but the valves of 

 that genus are described as being closed and free, while in 

 this there is a sinus in the margin, and probably it was an at- 

 tached shell. The teeth are generally three in number on 

 the shorter side, making an angle of 45° with the hinge-line, 

 and three on the longer side, w^hich are nearly horizontal. — 

 The shell is longitudinally striated, and the strice are cut by 

 elevated lines of growth, giving to the exterior a cancellated 

 appearance; the anterior side is rounded; posterior sub an- 

 gulated ; muscular impressions indistinct. 



