146 



broad and rounded, supcrior apex broadly rounded, margins straight. 

 Pseudoraphe indefinite, striae very fine, not less than 24-25 in 0.0 1 

 mm. Girdle face narrow, cuneate, with rather delicate margins, up- 

 per angles rounded. Septa superficial, very thin, straight, septal pun- 

 cta small, strongly marginai. Endochrome granular. Lenght 0.0295- 

 0039 mm., breadth of the girdle face 0.0073-0.0119 mm., breadth of 

 the valve 0.0095-0.0105 mm. 



Locality: California (Catalina Island near San Pedro), on Macro- 

 cystis, rather common. 



Differs from the type species, into which it gradually passes, by 

 the broader valves and the more delicate appearance of the frustule. 

 Some of the valves are of the same form as in L. pontica, but the 

 latter is much more robust and the girdle face is quite different. 



8. L Ehrenbergii var. fungoides Mer, [fig. 5]. 



Valve very broad. of the shape of a mushroom, composed of two 

 parts: the upper, very broad, conical, with rounded apex, very ah- 

 ruptly and sharply attenuated, passing into the lower part corres- 

 ponding to the stalk of the mushroom, this latter broadly linear, 

 becoming conical near the inferior end, which is slightly produccd 

 and somewhat acute. Pseudoraphe broad, striae very robust, radiate 

 near the superior apex, 7 in 0.0 1 mm, at the lower end, 7-8 in the 

 middle and 8-9 at the summit. Septa very shallow. Length o.iio- 

 0.124 mm., breadth of the upper part of the valve 0.039-0.0427 mm., 

 of the lower part 0.020-0.0256 mm. 



Locality: Kertsch (Crimea), fossil (Sarmatische Stufe', not rare. 



This curious form gradually passes on one side into var. subcon- 

 strìda Mer., and on the other into var. ovata (f. rhombica). 



The same fossil material from Kertsch contains a peculiar form 

 of var. ovata characterised by a more rhombical form of the valves, 

 with 7-8 striae in the middle which can be distinguished as var. ovata 

 forma rhomlnca. 



9. L. Ehrenbergii var. subconstricta Mer. [fig. 6]. 



Valve broadly elongated, more or less conslrìcted at the lower 

 end, more rarely in the middle, gradually broadening from this point 



