Naviculacea.'] INFUSORIAL animalcules. 353 



ture traversing the interior ; the exterior lamiua dissimilar, marked 

 by transverse lines; one external valve quite entire, the other Avith a 

 large pore at each apex. 



This genus, in being curved, approaches Achnanthes, but, by its 

 external and ' tabellar form, is still nearer Tessella ; its closest 

 affinity is with Bihlarium, which it resembles in internal structure. 

 It occurs in quadrangular tablets or boxes, made up of several 

 lamina, like the leaves of a book, but firmly connected. The lamina 

 or leaves are parallel with the narrow sides, and curved : the outer- 

 most leaflet on each side is thicker, like the cover of a book, and 

 marked with thirty-two horizontal striae. These two outer sculp- 

 tured lamina do not resemble each other as in Bihlarium, for one is 

 concave, and the other convex ; the concave one constitutes the 

 ventral surface, and has two large, round apertures at its two ends ; 

 whilst the other (cover or dorsum) possesses no opening. The in- 

 cluding or intervening leaves have each a large opening in the centre, 

 and, consequently, but a narrow margin is left; and the little tablets, 

 or boxes, have a continuous cavit^^ in their interior, such as also 

 occurs in Bihlarium. The sculptui'ed covers have a considerable 

 resemblance to Surirella. 



EuTOPYLA Australis. — Linear, landed at each end, in adult con- 

 dition with sixteen intermediate leaves, in young specimens often but 

 six ; external leaves (covers) marked (in the full grown state) by forty 

 Btriae (costse), bisected by a flexuous line, as in Siirirclla. Length 

 1 -240th. In 1843 Ehrenberg described this species imder the name 

 of Surirella (?) Australis. Found in Patagonian Guano. 



Genus Epithemja (Kiitz.) — Transverse section of lorica trapezoid, 

 transverse strite strongly marked, granular or moniliform. Locomo- 

 tion has not been observed. Both the upper and xmder surfaces are 

 traversed by two longitudinal Knes, terminated at each apex by a 

 pore. It belongs to the family Emiotioi, and differs from Navicula, 

 Cocconeis, Amphora, and Cymhella, by wanting a central opening, 

 and from Fragilaria, by its two sides being unlike, one being concave, 

 the other convex. Habitat, sea- water, on marine Algoe. 



E. Sorex. — Minute, dorsimi very convex, apices prominent, acute ; 

 striae onvergent, twelve in 1 1200111 ; figure on the primary side 



