406 ANIMAL NATURE OF DIATOME.E. 



titudes. Most of the freshwater species are perfectly 

 smooth. It is remarkable that the form of C. Pediculus 

 (C. Kiitzingce, Breb.) is conico-truncate; this is not noticed 

 by Kiitzing in his definition, much less in the figure, on 

 which account, before asking for his opinion of my own 

 specimens, I thought he was describing a different species. 

 Hence, in the duplication, the superior individual becomes 

 smaller than the inferior; and from the same condition 

 it results, that the margin appears bilineate when it 

 is simple, as Kiitzing figures it, and trilineate as the 

 same Kiitzing describes it in the specific definition, 

 when it is merely in the course of duplication. The 

 marine species display on their superior surface very 

 elegant transverse granulated striae, which either extend 

 across the entire breadth without interruption, or radiate 

 either from a median line or a central space. In only a 

 few species the striae are longitudinal, or concentric and 

 waved (flexuose). The ulterior characters by which the 

 thirty-four species of this most elegant genus are distin- 

 guished one from another, are still very slight. 



20. DORYPHORA. Lorica simplex bwalvis quadrangula 

 navicularis non concatenate, apertura in latere secundario 

 nulla ; linea suturali media longitudinali ; stipitata. 



The principal characters of the family are wanting in 

 the single species of this genus (D. ampkiceros.} Fixed 

 at one of its extremities by a stipes, and wanting the 

 central aperture in the secondary surfaces, it differs from 

 the Surirellce only by the continuity of the transverse 

 striae. In respect to the central aperture, Kiitzing 

 observes, that it may even be wanting in the Naviculce 

 themselves, and may be wanting in some individuals 

 though present in others of the same species. On a 

 character like this is based the difference of the orders. 

 With more right, and supported by numerous facts, I 

 can assert that there is a continuity of the striae in many 

 Suriretta. Hence I regard the Doryphora as allied to 

 these, and particularly to the Podocystida. 



