Surirellacece 



305 



Fig. 145. A, Surirella biseriata Breb., from Adel Bog, W. Yorks. (valve view, 

 x 400). B, S. linearis W. Sm., from Mickle Fell, N. Yorks. (girdle view, x 400). 

 C, S. robusta Ehrenb. var. splendida (Ehrenb.) V. H., from near Penzance, 

 Cornwall (valve view, x 400). D and E, Campylodiscus Hibernicus Ehrenb., 

 from Baildon, W. Yorks.; D, valve view; E, view showing the saddle-shaped 

 frustule; x 400. 



Genus Campylodiscus Ehrenb., 1841. The valves are ap- 

 parently irregularly circular, although in reality they are perfectly 

 circular. The apparent irregularity is due to their curvature, the 

 frustule being saddle-shaped. Each valve possesses a median 

 pseudo-raphe, and the pseudo-raphe of one valve is at right angles 

 to that of the other. The valves are furnished with costae, 

 generally short and often beaded. The genus is mostly marine. 



C. Echineis Ehrenb. and C. Hibernicus Ehrenb. (fig. 145 D and E) are 

 general but scarce in the freshwaters of the British Islands. Diam. of valves 

 about 100 p.. 



w. A. 



20 



