382 ANIMAL NATURE OF DIATOME^. 



species of Agardh (G. striatula, G. Jurgensii), adds, in 

 his work on Bacillarise, three marine species of Fragillaria 

 enumerated by Harvey (F. diatomoides, Grev., F. aurea, 

 Carm., F. Carmichaelii, Grev.), though with respect to 

 the last, Harvey himself objects to its position. I am 

 much more satisfied with the other plan suggested by 

 .Harvey, to place it in Striatella, for as the vittae are well 

 marked in this genus, the species seem to belong to it. 

 Kiitzing himself, in the Phycologia Germanica, united 

 the two species (striatula and Jurgensii) of Agardh into 

 one corresponding with the Artlirodesmus striatulus of 

 Ehrenberg, changed the named Grammonema into Gram- 

 matonema, and referred this genus to the Desmidiese. As 

 to the Frag, diatomoides of Greville, with which I was 

 favoured by Harvey, I think this conclusion right. It is 

 a true Desmidiean, for it has no siliceous shield. And it 

 is to be observed, that how perfectly soever it may 

 resemble the Fragillarice in form, it wants the longitudinal 

 canals and terminal perforations of the primary surfaces ; 

 and the internal substance is similar to that of the 

 Desmidieae. But as to the Con/erva striatula (E. B.), 

 Sowerby's figure certainly represents a Diatomean. 

 Wallroth has favoured me with a specimen thus named, 

 collected by Jurgens, and it proves to be a Grammato- 

 pkora. To the same genus, too, belongs the Diatoma 

 striatulum, supplied by Lenormand, whilst the Fragillaria 

 striatula, which I received from the same author, really 

 belongs to the genus Fragillaria, and corresponds per- 

 fectly with the F. virescens of Ralfs. So there remains 

 no small doubt in respect to this genus, which can only 

 be removed by a comparison of original specimens. 



9. DIATOMA. Individua (linearia) quadrangula, sym- 

 metrice formata, primum in fascias conjuncta, demum 

 soluta et per isthmum gelineum molle plus minusve dis- 

 tinctum angulis concatenata. 



The species with striated and perfectly linear frustules 

 (D. vulgare, D. mesodon, D. tenue,} are precisely similar 



