ANIMAL NATURE OF DIATOME^. 423 



36. Amphora. — Individua libera, singularia, aperturis 

 mediis birds lateralibiis, terniinalibus nullis I. obsoletis. 



The Amphorce are Cymbellce with primary surfaces 

 equal, and secondary surfaces symmetrically convex, 

 instead of plane and inclined. We have yet to learn 

 vphether the two median lateral perforations exist on one 

 part only or both. In the first case the analogy would 

 be complete ; in the second, every Amphora might be 

 called a double Cynbella. And indeed the two indivi- 

 duals into which every Amphora divides itself, by de- 

 duplication greatly resemble two Cymbellce. Yet perhaps 

 this resemblance is only apparent. In the Cymbella there 

 is one primary surface, the dorsal, which forms the 

 convexity. Again, in the middle of the Amphorce the 

 convexity is itself referable to that one of the secondary 

 surfaces which remains. The Cymbellce, in subdividing, 

 give origin to two complete individuals. The two indi- 

 viduals proceeding from the division of the Amphorce are 

 wanting in one of the two lateral convexities ; their lateral 

 surface, of new origin, ought to become convex, like the 

 other. In the Cymbellce there occurs a simple division 

 or deduplication ; in the Amphorce the division or dedu- 

 plication is succeeded by a species of reduplication. It 

 results, from this conformation, that in the Amphorce the 

 navicular figure is only apparently similar to that of the 

 Naviculce. The one is navicular in the secondary surfaces, 

 the other in the primary, because of the prominence of the 

 secondary. The division of Naviculce is parallel to the 

 elliptical or rhomboidal surfaces ; in the Amphorce it is 

 vertical to these (surfaces). I therefore absolutely exclude 

 the A. atomus from this genus, as it is a Navicula or a 

 Synedra. The doubt raised by Kiitzing as to the 

 A. ellipticce appears a certainty to me ; no central aper- 

 ture in the primary surfaces being admissible. On the 

 same motive I assert that if the A. acutiuscula do truly 

 belong to this genus, the figure 1 (PI. V, fig. 32) is 

 incorrect, for it represents a median aperture; and 

 equally so is the third figure (PI. XX, fig. 18) of the 



