TOXONIDEA. 



247 



Valve elliptical-lanceolate, with sub-acute apices ; raphe scarcely sigmoid, 

 surrounded by a small hyaline area, scarcely dilated round the central nodule. 

 Stria; fine, about 15 in c.d.m., difficult to resolve into beads ; connecting zone 

 scarcely oblique-twisted. Length, 8 to 10 c.d.m. 



Marine. Scheldt (H.V.H.) England (W. Sm. ! Kttton). Ireland (O'Meara). France 

 (Brebisson). Denmark, Holland (Van den Bosch). 



Note, Prof. Cleve forms S. latestriata into a new genus which he calls 

 Scoliotropis Cieve, while the two others remain in the genus Navicula. 



GENUS 20. TOXONIDEA DONKIN, 1858. 



Valves elongate, convex, with asymmetrical 

 margins ; striae decussate. Raphe arcuate with 

 its convexity turned towards the convex margin 

 of the valve. Frustules free. 



ANALYSIS OF SPECIES. 



Ventral margin straight, dorsal margin very 



arcuate, valve short thick set T. insignis . 



Ventral and dorsal margins feebly curved in 



opposite directions, valve long, elongate . T. Gregoriana. 



1 



{ 



Fig. 48. 



Toxonidea insignis. 



T. insignis Donkin (T.M.S., 1S58, vi., p. 



21, pi. 3, f. 2 ; H.V.H. Atl., pi. 17, f. 10* ; Type No. 



168), plate 5, fig. 256. 



Valve with dorsal margin strongly convex, 



ventral margin straight, apices strongly produced- 



rostrate on the dorsal side. Raphe strongly arcuate, 

 dividing the valve into very unequal portions. Striae decussate, reaching to 

 the raphe, 22 in 1 c.d.m. Length, about 10 c.d.m. Breadth, about 3 c.d.m. 



Marine. Washings of mussels (Debv) Blankenberghe. England (Kitton, Norman, Comber). 

 Scotland (Baxter, Coll., 1794). Ireland (O'Meara), and on all the coasts of the North Sea. 



T. Gregoriana Donk. (T.M.S., 1858, vi., p. 19, pi. 3, f. 1 ; Per., 

 pi. 9, f. 16*), plate 28, fig. 792. 



Valve very elongated, with apices produced-rostnte, margins slightly flexed 

 in opposite directions ; ventral margin nearly straight. Raphe dividing the 

 valve into two almost equal portion:. Striae decussate, reaching to the raphe, 

 the oblique 19 and the transverse 20 in 1 c.d.m. Length, 22 to 26 c.d.m. 

 Breadth, about 5 c.d.m. 



Marine. Blankenberghe (H.V.H.). England (Kitton, Comber). Ireland (O'Meara), and found, 

 but in small quantities, on all the coasts of the North Sea. 



