ANIMAL NATURE OF DIATOMEJS. 405 



greatest reduction of the terminal ones (inferior and 

 superior), such as we have in the Fragillarieae and the 

 Meridiem, but without the predominance of the primary 

 over the lateral, as in the former, what value these 

 characters have, in what relation they may stand to 

 internal organisation, I do not believe that we can decide 

 in the actual state of science. 



The five families (Eunotiece, Meridiea, Fragillariea, 

 Melosirete, Surirellece,} united together and arranged in 

 two groups, as they have the striae continuous (the first 

 three), or interrupted (the last two), constitute the order 

 Astomatica, or those wanting a character that is regarded 

 as essential to the following order. 



19. COCCONEIS. Individua singularia elliptica, de- 

 pressa, latere secundario foraminifero adnata, nunquam 

 stipitata, latere superiori media longitudinaliter impresso- 

 sulcato. 



The general form of Cocconeis is that of a disk of an 

 ellipsoidal figure, with surfaces more or less exactly 

 parallel, plane, or slightly curved. It corresponds, there- 

 fore, to the figure of Campylodiscus and the flexuose 

 Surirellce ; for in this genus, as in those, the secondary 

 surfaces prevail so much that the primary are reduced to 

 a simple margin. We know these to be the secondary 

 surfaces by the transverse or radiating stria3 with which 

 the superior surface in many species is marked, and by 

 the central perforation of the inferior surface ; and 

 because the division which is effected parallel to these 

 corresponds to the marginal fascia which represents the 

 primary surfaces. Contrary to all the genera hitherto 

 examined, it is precisely by one of these secondary sur- 

 faces that the Cocconeis adheres to those filiform algse, 

 on which it lives parasitically. Hence their resemblance 

 to the Epitliemite is only in appearance. The individuals 

 multiplied by duplication become quickly free, for it is 

 rare to find them geminate; but they soon adhere 

 parasitically to Alga3, and collect together in great mul- 



