48 MOLLUSCA FROM THE GREAT OOLITE. 



with an oblique sloping acute angle; umbones depressed, approximate, placed anterior 

 to the middle of the valves, radiating costae closely arranged undulated, slightly nodulated 

 and imbricated ; concentric folds numerous, rugose irregular and somewhat undulated ; 

 base sinuated. 



This species is exceedingly irregular both in its general figure and convexity, the portion 

 of the shell posterior to the carina is excavated and compressed, the lines upon its surface are 

 much knotted ; Area Prattii approximates to it but is less convex, and in that species the 

 lines are not nodose, neither has it the concentric undulating plications and sinuous base 

 which distinguishes the Area rugosa. It occurs somewhat rarely in the shelly beds of the 

 Great Oolite. 



Localities. Minchinhampton and Bisley Commons. 



Arc a minuta, Sow. Tab. V, fig. 11 a; Tab. VI, fig. 19. 



Cccull.ea minuta, Sow. Min. Con., t. 447, f. 3, 1824. 



Testa parvd trapeziformi, convexd, umbonibus acutis submedianis, subdistantibus, area 

 magna Icevigatd obliqud ; laferibus striis crebris radiantibus plicis incrementi interruptis. 



Shell small trapeziform, convex, with acute and rather distant umbones, area large, 

 smooth, sloping obliquely, the sides of the valves with densely arranged radiating striations, 

 broken by the concentric plications of growth. 



The figure of this little shell varies considerably in the size of the area, and in the 

 general convexity, the posterior angle is strongly marked, rather acute and slightly 

 concave ; the striations are only visible under a magnifier ; from two to ten lines appear 

 to be the amount of variation in length. It is not common, and is usually badly preserved, 

 its range is throughout the Great Oolite and Bradford clay of Gloucestershire. 



Localities. Minchinhampton ; Ancliff, Wiltshire ; Langrune, Normandy. 



Sub-Genus — Macrodon, Lycelt. 



Macrodox, H. E. Strickland and J. Buckman. Geol. of Chelt., 1845, p. 98. 



Testa subrhomboided, umbonibus anticis subremotis, area cardinali modice lata Icevigatd, 

 margine cardinali recto valde elongato ; latere antico convexo crasso, latere postico com- 

 pressiusculo, tenui et subtruncato ; margine inferiori corrugato, sinuato et hianle. Cardo 

 linearis, denlibus (5 — 7), anticis, angustis parallelis et obliquis; dentibus posticis plerumque 

 duobus, angustis, longitudinaliter elongatis ad extremitatem posticam testa product/*, 

 bipressio muscularis, anticus elevatus {id in Cucullcea instructa,) posticus obsoletus. 



Shell subrhomboidal, umbones anterior, rather distant, cardinal area moderately wide, 

 smooth, hinge line straight, and much elongated ; anterior side rounded and thick, posterior 

 side rather compressed, somewhat truncated and thinner, inferior margin corrugated in 

 its middle part, sinuated and gaping. Hinge linear, teeth (5 — 7), situated anteriorly, 

 narrow, parallel, and oblique ; posterior teeth usually two, narrow, elongated longitudinally 



