CYM BELLA. 



I 4 I 



ANALYSIS OF SPECIES. 

 I. Dorsal and ventral margins bent in contrary directions. 



Valve 

 broadly 



lanceolate 



or sub- 

 elliptic. 



Apices slightly produced . 

 Apices strongly rostrate-cuspidate 

 Apices rostrate-capitate 



C. Ehrenbergii. 

 C cuspidata. 

 C. amphicephala. 



Valve very 

 elongated 

 with dorsal 



margin 



much more 



arcuate 



than the 



ventral 



margin. 



Apices 

 imper- 

 ceptibly 

 attenuate. 



Apices obtuse ; raphe surrounded with a hyaline zone ; 

 stria; with well marked puncta . . . C. 



Apices sub-acute ; raphe without a hyaline zone ; strife 

 with puncta faint . . . . . C. 



f Ventral margin strongly gibbous in the median portion ; 

 raphe edged throughout its entire length with a broad 

 hvaline zone .... C 



Apices 



slightly 



rostrate or 



rostrate- 



subcapi- 



tate. 



Ventral 

 margin 



not 

 gibbous. 



Raphe very 

 marked 



arcuate, string distant, well 



obtusa. 

 pusilla. 



leptoceras. 

 amnis. 



f Apices 

 valve 

 sides 



rostrate - subcapitate ; 

 with almost equal 



C. subsequalis. 



Raphe 



almost 



straight ; 



strife 

 not well 

 marked. 



Apices strongly rostrate-capitate 



Valve elongate, 

 very narrow; dor- 

 sal margin slight- 

 ly arcuate ; strife 

 very delicate, 18 

 to 22 in 1 c.d.m. 



Valve rather broad, 

 with dorsal mar- 

 gin very arcuate ; 

 strife rather dis- 

 tinct about 14 in 

 1 c.d.m. 



Striae delicate 24 to 30 in 1 c.d.m. . 

 Strife robust about 14 in 1 c.d.m. . 



Apices 



slightly 



tapering, 



rostrate. 



C. delicatula. 



Valve naviculoid, sub- 

 lanceolate-linear mar- 

 gins scarcely bent, 

 almost straight, strife 

 delicate 



1 



I 



Strife approximate, valves with apices rostrate-capitate 

 Strife very distiant, apices scarcely contracted 



laevis. 



microcepbala. 

 tumidula. 



aequalis. 

 abnormis. 



II. Ventral and dorsal margins bent in the same direction: raphe bent 

 parallel to dorsal margin. 



Terminal 

 nodules not 

 very much 

 elongated. 



Striation not 

 interrupted 

 by a broad 



hyaline space 



on the 

 ventral side 



of the valve. 



Striation in- 

 terrupted by 



a broad 



hyaline space 



on the 



ventral side 



of the valve. 



Curvature of 

 raphe con- 

 siderable and 

 raphe bent 

 regularly 

 parallel to 

 the dorsal 

 margin. 



( Raphe surrounded with 

 a broad hyaline zone ; 

 strife with coarse 

 punctfe 



C. gastroides. 



Raphe with a narrow 

 hyaline zone ; strife 

 with puncta rather 

 fine 



C. lanceolata. 



Curvature of raphe inflected on the 



ventral side in the middle of the valve C. cymbiformis. 



Valves with apices for some length pro- 

 duced-rostrate ; central nodule usually 

 having a small furrow across it ; cen- 

 tral nodule often accompanied by one 

 or two isolated granules 



Apices obtuse, rounded, slightly or not 

 at all produced rostrate ; nodule sur- 

 rounded by 2 to 5 isolated granules 



Terminal ncdules very much elongated , 



C. tumida. 



C. Cistula. 

 C. Helvetica. 



