426 ANIMAL NATURE OF DIATOME.E. 



character of Naviculese, the central aperture, but even 

 the form of the shields corresponds to that of many 

 Synedrce of the sections Scaphularia and Eckinaria; 

 hence they seem rather to belong to the family of 

 Surirelleae in the preceding order. 



40. RAPHIDOGLGEA. Phi/coma glolosum gelineum 

 nolle, intus fasciculis navicularum in Jila radiantia 



The principal character of this genus is taken from the 

 amorphous disposition of the gelatinous substance, in 

 which the Naviculae, or rather the Synedree are immersed. 

 Under this point of view the genus Bcrkelcya is inter- 

 mediate between the Raphidoglcea and the Homceocladia. 

 But it is the characteristic disposition of these Synedrae, 

 that whilst they are mixed together in a disorderly 

 manner in the preceding genus, and fasciculated almost 

 in a parallel manner in the following one, in this they 

 are arranged in fusiform fasciae, confluent by the pointed 

 extremities. Whether we consider the first or the second 

 of these characters, I doubt whether we can regard them 

 as sufficient to distinguish the three genera. In one of 

 the four species enumerated by Kiitzing (E. manipulate) 

 the great variety in the size of the Synedrae is remark- 

 able ; he says they vary from ^rd to ^th of a line, but 

 with an amplification of 420 diameters he delineates 

 them from 7 to 25 millimetres, corresponding therefore 

 to 0-0166 millim. 0-0595 inillim. 



41. HOMCEOCLADIA. Phycoma fliforme ramosum, ex 

 gelineo intus fasciculis navicularum linearium 

 elongatarum bacillariarium farcto compositum. 



In confirmation of what has been already stated of the 

 difficulties attending the distinction of these genera, I 

 have subjoined the description of a new Homceocladia, 

 which in external figure bears a striking resemblance to 

 the Raphidofflosce, and in its association of filaments 

 might perhaps be referred to the Berkeley a. 



