426 ANIMAL NATURE OF DIATOME^. 



character of Navicnlese, the central aperture, but even 

 the form of the shields corresponds to that of many 

 Synedra of the sections Scaphularia and Echinaria ; 

 hence they seem rather to belong to the family of 

 Surirellese in the preceding order. 



40. Raphidoglcea. — Pliycoma glohomm yelinemn 

 yiolle, intus fasciculis navicularum in fila radiantia 

 disp ositis farctum . 



The principal character of this genus is taken from the 

 amorphous disposition of the gelatinous substance, in 

 which the Naviculse, or rather the Synedrae are immersed. 

 Under this point of view the genus Berkeleya is inter- 

 mediate between the Baphidoylwa 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 sufScient to distinguish the three genera. In one of 

 the four species enumerated by Kiitzing {B. manipulata) 

 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 millim. 



41. Homceocladia. — Thy coma filiforme ramosum, ex 

 tiibo gelineo intus fasciculis navicularum lineariuvi 

 elong alarum bacillariarium far do compositum. 



In confirmation of what has been already stated of the 

 difificulties 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 MapJiidoylcece, and in its association of filaments 

 might perhaps be referred to the Berheleyce. 



