NITZSCHIA. 391 



valve, and equally robust throughout their length ; striae about 18 in 1 c.d.m., 

 distinctly punctate. Length, about 4 c.d.m. 



Fresh water. Frahan (Delogne); England, France, Germany, etc; Scotland (Greville, 

 Hennedy). 



var. Tabellaria Grun. ! (Arct. Diat, p. 82 ; H.V.H. Atl., pi. 60, 

 f. 12 and 13*; Type No. 386), plate 15, fig. 517. 



Valve very inflated in the median portion, with apices longly diminuate 

 rostrate; costoe 6'5 to 7*5 in 1 c.d.m.; striae 21 or 22 in 1 c.d.m., 

 delicately punctate. 



Fresh water. Brussels (Delogne). 



Group 10. SCALARES. 



Distinguished from the preceding groups by the keel being more 

 acute and less eccentric. 



N. scalaris W. Sm. (S.b.d., i., p. 39 , pi. i 4 , f. 115 ; h.v.h. Atl., 



pi. 60, f. 14-15* ; Type No. 387), plate 32, fig. 874. 



Valve broadly linear, with conical apices, costs of unequal length, 3 to 5 

 in 1 c.d.m.; transverse striae narrowly punctate, 9 to 1 1 in 1 c.d.m. Frustule 

 in transverse section quadrate or in form of an oblong square. Length, up to 

 48 c.d.m. Breadth of valves, 2 to 2*5 c.d.m. 



Brackish water. England (W. Sm., Norman, Stolt. ), France (De Breb.), Denmark (Heiberg). 



Group 11. Insignes. 



Similar to the forms of the preceding group, but with a keel still 

 more eccentric and frustules sometimes somewhat sigmoid. 



N. insignis Greg. (T.M.S., 1857, v., p. 80, pi. 1, f. 46; H.V.H. 



Atl., pi. 61, figs, various*), plate 32, fig. 875. 



Valves linear, lanceolate, with apices subconical, produced, keel almost 

 central, broad, straight or gently curved. Costae rather long, 4 or 5 in 1 

 c.d.m. Striae, 10 or 1 1 in 1 c.d.m., strongly punctate. Frustules straight, 

 linear. Length, up to 40 c.d.m. 



Marine. Coasts of England (Norman), and Scotland (Gregory). 



var. Smithii. (A 7 , spectabilis W. Sm.; H.V.H. Atl., pi. 61, f. 4*), 

 plate 32, fig. 876. 



Distinguished from the type-form by being slightly sigmoid; costae 

 short, 2 or 3 in 1 c.d.m. Striae 13 or 14 in 1 c.d.m. 

 Brackish water. England (Norman), France (De Breb). 



