COSCINODISCUS. 



525 



conspicuous fascicles, preudo-nodule indistinct. Centre with puncta in 

 irregular concentric rows. Striae about 16 in 1 c.d.m. near the middle of the 

 ray ; length of minor axis of valve, 3 to 4 c.d.m. ; major axis 4 to 6*5 c.d.m. 



Marine. France (Normandy, Breb!), England (Deby, Norman), Scotland (W. Arn. ! 

 Rattray). 



Sect. V. Eucoscinodisce^:. Valves with similar structure 



throughout the surface. 

 GENUS 187. COSCINODISCUS EHR, 1838. 



Fig. 278. Coscinodiscus 

 excentricus. 



Fig. 277 .Coscinodiscus Asteromphalus var. consticua. 



Valves circular or elliptic without any process (sometimes with 

 small submarginal teeth), costae or septa. Structure alveolate or 

 punctate. Frustule disciform. 



The genus Coscinodiscus is in a more confused state than any other. It 

 comprises not less than 300 species, on the value of which authors are far 

 from being agreed. The genus has been the subject of three important 



