36 



RHABDONEMA. 



GENUS 71. RHABDONEMA KUTZ, 1844. 



Valve lanceolate or linear, with pseudo-raphe distinct, apices 

 usually smooth, furnished with costal or robust beads. Girdle face 

 showing numerous false septa. Frustules united in filaments, shortly 

 stipitate. Endochrome granular, sparse. 



The genus includes about 15 species, living or fossil, but only three belong 

 to our shores. 





Fig. in. Khabdonema arcualum. 



ANALYSIS OF SPECIES 



f . ,, , , r f False septa having only a single perforation ; 



Girdle face showing fine valves furnished with costal alternate with 



beads alternating with mon iliform strise . . . R. arcuatum. 



transverse costce ; "1 

 valves with smooth j Fa]se septa having three perforations . valves 



a P lces - |_ furnished with costse, resolvable into beads . R. Adriaticum. 



_ Girdle face not showing transverse costas ; valves entirely striate 



. R. minutum 



R. Adriaticum Kiitz. (Bac, p. 126, pi. 18, f. 7; h.v.h. Atl, pi. 



54, f. 11-13* ; Type No. 360), plate 12, fig. 486^. 



Valves narrow, linear elliptic, with apices smooth, showing false costae, 

 8 to 9 in 1 cd.m., which can be resolved into approximate beads. False 

 septa with three openings, furnished with transverse costos and a pseudo- 

 r.iphe. Girdle face shewing numerous false septa, the intervals between which 

 are filled with transverse costas (7 or 8 in 1 cd.m.), and between each of 

 which are found one or two rows of very fine puncta. Length, 6 to 9 cd.m. 

 Breadth, up to 20 cd.m. each frustule. 



Marine. Not yet found in Belgium. England (Norman, W. Sm.). Scotland (Arnott), 

 Ireland (W. Sm. , O'Meara). France, Bahnsie, Sweden, &c. 



R. arcuatum (Agardh) Kutz. (Bac, P l. 18, f. 6; h.v.h. Atl, 



pi. 54, f. 14-16*; Type No. 361), plate 12, fig. 487^. 



