ANIMAL NATURE OF DlATOMEjB. 431 



which he pronounces synonymous with the Naunema 

 JDillwynii of Ehrenberg. In this he says the Naviculse 

 are ^" long, or 0'0246 milHm. ; but he represents 

 them 5 milHm. with a power of 420, corresponding 

 therefore to 0012 millim. Here again there is ground 

 for the same consideration, as to the slight difference 

 we should meet with between the size of the figures 

 and the admeasurement, were the latter understood 

 as expressed conventionally in lines equal to two mil- 

 limetres. It seems to be so from the figures of 

 Lyngbye and Greville, but not from either of the two 

 species of Kiitzing. We are led to this supposition by 

 an observation of Harvey, who says, that in the M. qua- 

 dripunctatum the Naviculse are larger than in any other 

 English species, whilst by Klitzing's description, and still 

 more by his figures, there would seem to be only two of 

 these in which the Naviculse are of smaller dimensions. 

 Harvey says, that specimens from Carmichael differ in 

 external appearance from those of Mrs. Griffiths, though 

 agreeing as to internal structure. 



I received from Lenormand a specimen from Calvados, 

 with the name Schizonema quadripunctatum, in which the 

 length of the Naviculse was 0-024'". 



Here it seems right to mention some different species, 

 all belonging to the genus Monnema. 



Monnema tenuissimum, Kiitz., (Schizonema.) 



Having been favoured by Kiitzing with an authentic 

 specimen of this his species, I could with certainty 

 compare it with specimens from Venice sent to me by 

 Kellner. I have ascertained that the length of the 

 Naviculse = 0'022 millim. This would agree sufficiently 

 with that indicated by Kiitzing in the description, where 

 he says it is yjoth of a Paris line, or ^ 0"0246 mUhm. 

 But he figures these Naviculse with an amplification of 420, 

 no more than 4'5 millim. which corresponds to O'OIO? 

 millim. Here it seems, then, that the measurement 

 expressed in the description ought really to be understood 



