4^4 



DITYLUM. 



GENUS 90. DITYLUM BAILEY, 1861. 



Valve angular, furnished with a long cen- 

 tral spine, with radiant puncta. Frustules 

 distant, slightly silicious, with undulated 



margins. 



ANALYSIS OF SPECIES. 



f Striae excessively fine ; valves not bordered 



with indentations . . . . D. intricatum. 



I Striae well marked ; valves bordered with 



I indentations D. Brightwellii. 



D. Brightwellii (West) Grun. 



{Triceratiam Brightwellii, IV-st., T.M.S., 1858, 

 viii., p. 149, pi. 8, f. 1, 5 and 8; D. trigonum 

 and ina-auale Bail. ; Triceratium undulatum, 

 Brightw., Q.J.M.S., 1858, vi., p. 153, pi. 8; 

 H.V.H. At!., pi. 114, f. 4, 8 and 9*; in Type No. 

 529) plate 17, fig. 606, 



Valves triangular or tetrangular, with margins 

 straight or undulated, furnished with small spines, 

 somewhat elevated in the centre, and bearing a 

 long spine, surrounded by a small narrow hyaline 

 area; striae radiant (12 in 1 c.d.m. at the margin 

 of the valve), with very distinct puncta. Girdle 

 face with connecting membrane apparently smooth. 

 Breadth of side of frustule about 3^5 to 4*5 c.d.m. 



Marine. Blankenberghe, rare ; very abundant in some 

 pelagic gatherings from the Scheldt (H.V.H. ). England (W. 

 Arnott ! Kitton), 



Fig. \\\.Ditylum Brightwellii. 



D. intricatum (West.) Grun. {Triceratium intricatum, West., 

 T.M.S., 1858, viii., p. 148, pi. 7, f. 5 ; H.V.H. Atl., pi. 114, f. 2*), plate 17, 

 fig. 607. 



