NITZSCHIA. 393 



N. Petitiana Grim. (H.V.H. Atl, pi. 62, f. 6*), plate 16, 

 fig. 520 



Valve small, with ventral margin straight, dorsal margin very gently and 

 regularly attenuate up to the apices, which are rostrate. Carinal dots 8 or 9 

 in 1 c.d.m., scarcely prolonged. Striae delicate, about 27 to 30 in 1 c.d.m. 



Brackish water. Not yet found in Belgium. 



Group 14. SPATHULATA. 



Analogous to Bacillaria from which it is differentiated by the very 

 delicate striation of the valves and by two auxiliary lines parallel to 

 the keel. 



ANALYSIS OF SPECIES. 



I Girdle face showing the apices of the keel enlarged and elevated . N. spathulata. 



f Valve with apices longly rostrate . . . N. cursoria. 



-j t- . I Valves f Carinal dots, 1-5 to 3 in 1 c.d.m. ; apices some- 



I , ! , -: with what produced . N. distans. 



elevated ' 



apices -; 



not j Carinal dots. 3 '5 to 5 in 1 c.d.m. ; apices not 



t, costrate. l. produced . . . N. angularis. 



N. angularis W. Sm. ! (S.B.D., i., p. 40, pi. 13, f. 117 ; H.V.H. 

 Atl., pi. 62, f. n-14*), plate 16, fig. 521. 



Valve narrowly lanceolate, very gently attenuate up to the subobtuse 

 apices. Valve with keel central, 3 "5 to 5 marginal dots in 1 c.d.m. ; auxiliary 

 lines clearly visible; transverse striae delicate, 31 or more in 1 c.d.m., formed 

 of puncta which equally produce longitudinal and oblique striae. Girdle face 

 broadly linear, somewhat inflated at the median portion, with connecting zone 

 plicate. Length, 6 to 20 c.d.m. ; breadth of valves, about 1 to 1*5 c.d.m. 



Marine. Washings of Mussels (Deby). England (W. Sm. ! Comber, Norman), Ireland 

 (O'Meara), Scotland (Baxter Coll., No. 2765). 



var. affinis Grun. (H.V.H. Atl., pi. 62, f. 16*), plate 16, fig. 

 522. 



Differs from the type-form by its smaller size (3 to 9 c.d.m. in length) 

 and its more approximate carinal dots (6 to 9 in c.d.m.), and its still 

 finer striae. 



N. spathulata Breb. (in w. Sm., S.B.D., i., p. 4 o, pi. 31, f. 268; 



H.V.H. Atl., pi. 62, f. 7 and 8*; Type No. 390), plate 16, fig. 523. 



