ANIMAL NATURE OF DIATOME.E. 399 



merely distinguished from Synedra because they are not 

 affixed, we find the Podocystida stipitate and affixed. 

 Yet do I intend to maintain that it is not allied to the 

 other Surirellce. I only notice how vacillating are the 

 principles of the proposed classification. The Podos- 

 phenia of Hassall, excluding the synonyms, seems to 

 belong to this sub-genus. 



17. BACILLARIA. Individua bacilliformia prismatico- 

 rectangula, linearia, primum in seriem rectam tabulatam 

 transversim conjuncta, dein in series obliquas dimota. 



The singular appearances assumed by the only species 

 of this genus (B. paradoxa) and the liveliness of its 

 motions have long been celebrated (Muller). The prin- 

 cipal organographical character that distinguishes it from 

 the Fragillarice is the same that allies it to a different 

 group of the family, viz., the interruption of the trans- 

 verse striae in the median line of the secondary surfaces, 

 to which is added the parallelism of the primary surfaces. 

 Hassall overlooked the former of these characters in the 

 figure he gave of this species. The physiological cha- 

 racter of mobility of the frustules, and the symmetrical 

 disposition which they assume, becomes the more im- 

 portant, inasmuch as they do not recur in any other 

 Diatomese ; and therefore we believe that they merit this 

 particular mention. 



18. SYNEDRA. Individua bacillaria, prismatico-rec- 

 tangula, demum uno vel altero fine adnata ; latus secun- 

 darium primario <equale, vel angustius, linea lavissima 

 media longitudinali per cur sum. 



* Scaphularia. Minutce, rarissime adnatce, lavissimce; 

 (non transversim striatte.} 



The eleven species enumerated in this sub-genus are 

 only classed together by negative characters, viz., the 

 want of the characters of other genera more or less allied. 

 In general it is only required that they should have their 

 secondary surfaces marked with transverse striae, either 



