470 DESCnil'TloN OF {Polygastrica. 



short horns, and a very short central process. Among Conferva, 

 Heligoland (P. 16, figs. 30, 31, 32, 32a.) 



Odontella aurita = Benticella gracilis (Ehr.) and Biddulphia aurita 

 (Ealfs.) — ^^''ery minutely punctate, with a broad central band, ex- 

 tended, slender, acute horns, and a large middle process. Among Algae, 

 British Coast and Baltic. 



0. turgida = Denticella turgida (Ehr.) — Large, very finely punc- 

 tate ; horns recurved, large, obtuse, and a broad, round, central 

 process. North Sea. 



0. polymor-pha = Biddulphia lavis (Ehr.) — Large, with minute, 

 obtuse horns, and no central process. 



Genus Oncosphenia. — Lorica simple, quadrangular, cuneate, not 

 concatenate ; valves without a central umbilicus, and also destitute 

 of lateral apertures and internal septa ; equal, but their apices 

 unequal, on account of their cuneate and uncinate form, Oncosphe- 

 nios approach nearest to Podosphenice, by the absence of pedicles in 

 the latter, but are peculiar in their uncinate form. 



0. Carpathica. — Cuneate on the sides and striate ; one end straight, 

 turgid, and rounded ; the other attenuate and uncinate. Diameter 

 1- 792nd, Tvdth eleven pinnules. On the back, their quadi'angular 

 figure resembles that of a wand of ten Bacillaria. Carpathian 

 mountains. 



Genus Pododisctjs, (Kvitz.) — Frustules single or concatenate, 

 stalked ; primaiy side obsolete ; secondary side convex, stipes lateral. 

 It approaches very closely to Podosira ; but the stalk is placed on 

 the circumference of the disc and not at its centre, as in the latter. 

 It is a member of the family Melosirce. 



P. Jamaicensis. — Single, or in chains, smooth ; stalk long, delicate. 

 Diameter 1 -840th. (P. 16, f 28.) On AlgSD. 



Genus Podosiea. — Concatenate, very distinctly stalked ; apparently 

 bivalve, convex, nearly round ; stipes central, self-division imperfect, 

 giving rise to moniliform chains. (The two valves are approximated 

 without the presence of any intermediate ring ; hence, in Kiitzing's 

 language, the primary side, as in Pododisciis, is wanting — obsolete.) 

 The valves of the two species are very finely punctate. The lorica 

 is soft or homy ; the stalk is more developed than in GallioneUa, 



