856 DESCEIPTION OF {Polygastrica. 



concave, dorsal convex, and often dentate, with two apertures at each 

 apex; lateral sm-faces plane. Sell-division complete, and hence the 

 frustules are always solitary, or in pairs, during the process of fission. 

 Found both living and fossil. Habitat, freshwater, parasitic on 

 Algae. 



Eiinotia is closely allied to Nmicula, but differs in the absence of 

 a central opening (umbilicus.) The cross section of the lorica is 

 trapezoid, and the transverse sti'ise ai'e uninterrupted, i. e. unbroken, 

 " The frustules are simple or binate, quadrangular." 



Eunotia are mostly found attached, by their concave surface, to 

 various fresh water Algas. 



" Some species," says Mr. Ealfs (Ann. Nat. Hist. 1844, p. 459), 

 placed by Ehrenberg in this genus, have cymbiform frustules, and 

 belong to Agardh's genus Cymhella. 



" In Eimotia the finistules resemble those of some species of Fragi- 

 laria, but are not united into a filament. Viewed laterally the frus- 

 tules are lunate. The convex dorsal surface is generally raised in 

 transverse ridges (dentations, Ehr.) ; and the number of these ridges, 

 as seen in a lateral view, when they appear like teeth, distinguishes 

 the species. Prof. Bailey suspects that the number of these teeth is 

 liable to variation, and that the'* number of species has, in conse- 

 quence, been made too great." 



Besides multiplying by self-division, the Eunotim have been 

 observed by Mr. Thwaites, and others, to propagate by conjugation. 

 (P. 14, f. 1 to 8.) Frustules developed in the latter mode are larger 

 than the parent beings producing them, and in their early stage are 

 siu'rounded by mucus, and not striated. "Where the number of 

 dentations is equal in two forms, and so cannot furnish a specific 

 character, then the variations in the figure of the lorica generally, 

 and particularly of its apices, are employed. 



Etjnotia turgida. ^= Epithemia turgida (Kutz.) — Lorica semi- 

 lanceolate; ends truncate; striated; striae eight in 1-1 200th. 

 Dorsum convex. A longitudinal furrow runs along the middle of each 

 side ; scarcely visible in living specimens, owing to the colour of the 

 body. (Group 157, P. 3, and f. 158, 159, 160, and 161, P- 14, 

 f. 1 to 8.) Foimd upon Vauchcria and Conferva. Length 1-11 50th. 

 to 1 -240th. 



