222 DESCRIPTION OF [Polygastrica. 



a fallow or greenish hue. Breadth of band 1 -480th to 

 l-5?0th. 



297. FRAGILARIA scalaris. The ladder-like Fragilaria 

 is smooth, and seven to eight times longer than broad ; 

 ova of a fallow hue. Breadth of band 1 -860th to l-570th. 



298. FRAGILARIA diopthalma. The two-eyed Fragilaria 

 is smooth, and three or four times longer than broad ; 

 ova of a yellow golden colour, disposed in two portions. 

 Length l-960th to l-1150th. 



299. FRAGILARIA pectinalis. The comb-like Fragilaria 

 is striated, and two to four times longer than broad. This 

 species is swelled and lanceolate upon the lateral surface, 

 and has eight striae ii> l-100th of a line; ova of a yellow 

 hue. In the living state, the striae are very indistinct. 

 Group 176 exhibits a band of five specimens, with indica- 

 tions of stomach- cells, and the side view of a single one. 

 Found both recent and fossil ; the latter in the Isle of 

 France, and in Bergmehl, in Sweden. Length l-2200th 

 to l-430th. 



Genus LXIV. MERIDION. The fan little wand Animal- 

 cules. The characters of this small genus differ from 

 the preceding only in the mode of aggregating during self- 

 division, which is in the form of a volute or spiral, occa- 

 sioned by one end being broader than the other. In 

 organization, they are closely allied to Navicula, except 

 that they have two openings at the broad end only. 

 Ehrenberg says the ova cluster is four-leaved, and nume- 

 rous stomach-cells are seen ; single wands of both these 

 species are difficult to distinguish from species of Gompho- 

 nema; but the latter, it should be remembered, have a 

 middle opening, as well as two anteriorly. 



