MASTOGLOIA. 



GENUS 4. MASTOGLOIA. THWAITES, 1848. 



T 53 



Frustules naviculoid, most frequently enclosed in a gelatinous 

 envelope, with valves furnished with loculi or marginal cells formed of 

 silicious plates interposed between the connecting membrane and the 

 valve, to which they most frequently appear to be adherent. 



Fig. 28. ( 1 2 J .1/. lanceolata Tht. ; fjj .1/. Smifhii T/iw., var. lacustris Grun. 



ANALYSIS OF SPECIES. 



Valves 

 with striae 

 not inter- 

 rupted by 



sulci, 

 making to- 

 gether the 

 figure of a 



lyre. 



Valve 



lanceolate, 



with loculi 



arranged 



in an 



arcuate 



row. 



Valve 

 linear- 

 elliptic 

 with loculi 

 arranged 



in a 



straight 



row. 



More 

 than five 



loculi 

 with out- 

 line not 

 rounded. 



Strias 



radiant 



up to 



the 



apices of 



the 



valve. 



Loculi rather broad, 

 occupying almost 

 half of the margin 

 of the valve 



Loculi narrow, very 

 numerous, occupy- 

 ing almost the 

 entire outline of 

 the valve . 



Strire almost parallel at the mid- 

 dle of the valve, convergent at 



apices 



3 to 5 loculi, with 

 rounded outline . 



( Strias rr- 

 gent 



radiant, diver- 



-! 



Striae radiant, con- 

 vergent 



Apices abruptly attenuate ; striae finely 

 punctate ; marine or brackish 



Apices cuneate ; striae with coarse puncta ; 

 fresh water .... 



M. Smithii. 



M. apiculata. 



M. lanceolata. 



M. exigua. 

 M. Closeii. 



M. Dansei. 



M. Grevillei. 



Valves with striae interrupted by sulci, making together the figure of a lyre M. Braunii. 



