GERVILTJA. 



75 



is slightly convex or sometimes almost straight ; on this part the growth-lines are 

 convex posteriorly and cnrvc towards the nmbo, except in young specimens where 

 tla-y curve posteriorly as thoy approacli the hinge-line. 



Hinge-line long, forming rather less than half the greatest length of the valve, 



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\SJ 



^S'l 



He^ 



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FiQ. 7.—Gernllia suhlanceolata (d'Orbifpiy.) Lower Gieonaaml (Crackers), Athorfiold. Seilj^ict Museum. 

 X j. a, left valve ; b, antero-dorsal view of another specimen ; c, left valve of another specimen. 



and making an obtuse angle with the posterior margin. Ligament pits large, 

 usually from six to nine in number, placed at nearly equal distances, and usually of 

 nearly equal size, except the anterior and posterior, whicli may be smaller than the 

 others. 



Surface of valves ornamented with growth-lamellae only. 



