ANIMAL NATURE OF DIATOME^E. 429 



rejects it as erroneous, and substitutes in its stead a new 

 name (Naunema) applicable to the two genera which he 

 reunites. It is doubtful whether the right of priority 

 ought to be assigned to the Hydrolinum of Link, which 

 along with a Moncma, comprised an Alga (Conferva 

 llernianni), and therefore cannot be considered suf- 

 ficiently definite. The name Monema, which on account 

 of its elision should be written Monnema, applied to the 

 species constituted of a single tube including the 

 Naviculae, and placed in comparison with the rest, 

 (Schizonema}, referable to the species where the single 

 series of Naviculae have a proper tube, and the union of 

 these threads (fili) constitutes the frond, is so much the 

 more exact since the second, Schizonema, both by ety- 

 mology and generic character of Agardh himself, as 

 mentioned already, (Systema Algarum, 1824,) denotes 

 this condition in a graphical manner. There is still an 

 important character described by Kiitzing in reference to 

 the position of the organs which he terms spermatia. 

 These are external in Monnema (Schizonema}, immersed 

 again in the Schizonema (Micromega), as if intimately 

 allied to the simple or compound structure of the external 

 tube. Now after the consideration of such characters, 

 the result of an attentive examination is my conviction 

 that some species referred by Kiitzing to the first of 

 these genera belong really to the second ; and, for the 

 reasons just stated, these will be all entitled to the name 

 assigned by Kiitzing, whilst all the other species of 

 Schizonema should become Monnema, and those for 

 which the name Micromega was uselessly created, should 

 become Schizonema. 



This discordance of opinion as to the arrangement of 

 some species in one or other of the two genera, which, 

 independently of their names, appear so distinct and so 

 clearly defined, arises from the great difficulty of dis- 

 cerning the parallel tubes, including the particular (sin- 

 gole) series of Naviculae. In some species the wall of 

 the external tube is clearly distinct, and the Naviculae are 



