3 68 



SURIRELLA. 



GENUS 78. SURIRELLA TURPIN, 1827. 



Valves cuneate, reniform, elliptic or linear, sometimes twisted, 

 having a pseudo-raphe linear or lanceolate ; furnished with costse, 

 short or reaching to the pseudo-raphe, and a submarginal keel of 

 greater or less size ; pseudo-raphe parallel in the two valves. Girdle 

 face showing alae produced on the projecting keel. 



Fig. 120. Surirella biseriata. 



Endochrome formed of two layers, each of which rest flat about 

 the middle, on the interior side of the valves. 



