large, strongly marginai, secondary puncta absent. Endochrome gra- 

 nular (6-12 granules). Length 0.0214-0,0460 mm. (usually o.o33 mm.), 

 breadth of the girdle face 0.0 1 3-0.019 mm., breadth of the valve 

 0.0072-0.0082 mm. 



Locality : Black sea (lalta, Theodosia in Crimea), rare. 



This is the only species with rounded inferior apex of the fru- 

 stule; it is intermediate between L. ovuluni and L. duina as the lat- 

 ter is intermediate between L. pontica and L. Jiirgensii, these 

 four species thus forming a continuous genealogical line without in- 

 tcrruption. 



3i. L. proboscidea Mer. [fìg. 22]. 



Valve narrow, davate, abruptly attenuated in its superior part, 

 terminating in a long, narrow proboscis or rostrum, gradually atte- 

 nuated towards the very narrow and acute end lower margins 

 straight or slightly concave. Striae very fine, 24 or more in 0.0 1 

 mm. Girdle face cuneate, rather narrow, with upper angles acute 

 or subacute, margins thin; septa deep (o.oo56 mm.), strongly ar- 

 cuate and divergent towards the upper apex, septal puncta very 

 small, round, distinct. Forming small colonies on short dichotomeo- 

 usly ramified stipes which are composed of a darker axial part and 

 a lighter external layer. Length o.o38-o.o56 mm , breadth of the 

 girdle face 0.0086-0.020 mm., breadth of the valve 0.00285-0.0048 mm. 



Locality : Adriatic (Pola), not rare. 



This species is rather variable in its characteristics; the rostrum 

 is more or less narrow and more or less distinctly separated from 

 the rest of the valve; the breadth of the frustule and the depth of 

 the septa are also subject to variations. The shape of the valves is 

 almost the same as in L. rostrata Mer., although both are very di- 

 stinct species, their size, girdle face and striae bcing quite different. 

 Has a great aljinity with L. semiasymmetrica Mer. 



