LITHODESMIUM. 



465 



(Western Scheldt) ; then in the August of the same year, I obtained a very 

 abundant pelagic gathering in the Eastern Scheldt, between Ouwerkerk and 

 the red buoy of Sandcreek (Holland). 



This species, therefore, does not appear to be excessively rare, but entirely 

 pelagic, and found only at certain periods of the year. 



GENUS 131. LITHODESMIUM EHR, 1840. 



go8$* 



a. h. 



Fig. 196. Lithodesmium undulatum, 

 a. Valve view. b. Girdle view. 



Valve triangular, with angles inflated, raised and terminated by a 

 robust awn. Frustules very slightly silicious, united into a long 

 filament, and connected with one another by a cellular membrane. 



L. undulatum Ehr. (Kreideth, p. 75, No. 49, pi. 4, f. 13; H.V.H. 

 Atl., pi. 116, f. 8-1 1* ; Type No. 506), plate 19, fig. 627. 



Valve triangular, with undulated margins, apices raised and ending in a 

 robust awn, simple or bifurcated , centre elevated and furnished with a strong 

 spine ; stria; delicate (about 10 to 14 in 1 c.d.m. at the margin of the valve), 

 radiant, finely punctate. Length from one apex of the valve to another, 4 to 

 6 c.d.m. Girdle face quadrangular, connecting zone with excessively delicate 

 longitudinal striae, about 20 in 1 c.d.m, interrupted by transverse hyaline lines. 

 Frustules united into a filament and closely connected to one another by a 

 membrane marked with coarse puncta in quincunx, and forming 10 to 12 

 longitudinal striae in 1 c.d.m. 



Marine. Not rare. Blankenberghe in the 2nd Basin. 



GG 



