ENCYONEMA. 1 49 



Frustules generally enclosed in tubes. Valve more or less cymbi- 

 form, divided unequally into two parts by the raphe and the central 

 nodule, which is eccentric. Raphe straight. Terminal nodules con- 

 siderably distant from the apices. Endochrome as in the Amphora. 



ANALYSIS OF SPECIES. 



Raphe surrounded by f Apices broadly obtuse, rounded. . E. prostratum. 



a hyaline zone inflated j 



round the central no- \ 



dule. V Apices acute . . . E. turgidum. 



f Ventral portion of valve rather broad ; 

 ventral margin rather strongly inflated, 

 Hyaline zone not in- J specially in the median part . E. caspitosum. 



fkled round the cen- j .- , , 



tral nodule entral portion very narrow ; ventral 



margin straight or concave, rarely a little 

 I gibbous . E. ventricosum. 



Length of 

 valve never 



exceeding 

 3 to 4 times 

 its breadth. 



Valves very f Striae very conspicuous, distant, having the same length throughout, 

 elongated, ventral margin concave . . . . . . E. lunatum. 



length 5-9 -J 



times its Striae fine, approximate, shorter near the central nodule ; ventral 



breadth. l_ margin straight, or inflated in the middle . . . . E, gracile. 



Sect. I. Length of valve never exceeding three to four times its breadth. 

 Raphe surrounded by a hyaline zone, inflated round the central nodule. 



E. prostratum Ralfs ! (Ann. & Mag., vol. i6,pl. 3, f. 3; H.V.H. 



Atl. pi. 3, f. 9, 10, 11*; Type No. 34); plate 1, fig. 44. 



Valve large, with dorsal side considerably inflated, ventral side with slight 

 curvature ; apices abruptly produced, obtuse, straight, recurved on ventral 

 side ; raphe straight, with its median ends slightly arcuate towards the dorsal 

 margin, surrounded by a hyaline zone, broad and strongly inflated round the 

 central nodule ; terminal nodules very large and extremely elongate towards 

 the dorsal margin, completely surrounded by stria?, except where they touch 

 the raphe; striae 6 or 7 in 1 c.d.m., robust (simulating costae), divided cross- 

 wise ; some near the central nodule being often only half as long as others. 

 Length 6 to 9 c.d.m. 



Fresh water. Almost everywhere. 



E. turgidum (Greg.) Grun. ! (Cymbella turgida Greg. Q.J. M.S. 



1856, p. 5, pi. 1, f. 18; H.V.H, Atl. pi. 3, f. 12*), plate 1, fig. 45. 



Valve cymbiform with dorsum very convex, venter almost straight, some- 

 what inflated in the middle ; apices sub-acute ; raphe straight, surrounded by 



