ARNOTT, ON CYCLOTELLA. 247 



3. C. Kutzingiana ; ends of frustule undulate ; centre of 

 valve convex, but neither striate nor bullate ; marginal striae 

 long, coarse. 



4. C. operculata ; ends of frustule undulate, centre of 

 valve convex, but neither striate nor bullate; striae short, 

 close. 



5. C. minutula ; ends of frustule flat; centre of valve with 

 radiating clots or striae. 



To C. Dallusiana I refer C. radiata of Brightwell. I 

 possess what I consider to be C. Meneghiniana from a stream 

 that empties itself into Bidston Marsh, Cheshire, where it 

 was collected in August, 1858, by Mr. T. Comber; but 

 it is not noticed in his " Catalogue of Liverpool Diatoms," 

 ' Mic. Journ./ viii, p. 113), unless it be what he calls 

 C. Kutzingiana, ft* Mr. G. Norman, of Hull, has also found 

 it in the pond of the botanic garden there, and in some other 

 places about Hull ; but in all these localities it is very sparse, 

 and much mixed with other diatoms. I have not seen a 

 good frustule with the front view from England, but I 

 do not think that any doubt can be entertained about the 

 species. 



C. Rotula, Sm., from deposits, sometimes approaches 

 closely to C. minutula, but has distinctly moniliform striae, 

 and when recent has a series of small, broad-topped, nail- 

 like, spinous processes close to the margin, and perpendi- 

 cular to the surface of the valve ; these are easily broken 

 off, and this affords one of the many arguments against 

 drawing up specific characters from specimens obtained from 

 deposits ; the latter may, by ocular comparison, and even 

 by written characters, be frequently correctly referred to 

 the recent form, but recent ones can rarely be satisfactorily 

 determined from descriptions made only from the abraded 

 state. C. Rotula, Sm., is C. Rotula, Kiits. ( f Bac./ tab. ii, 

 fig. 11) ; but as Ehrenberg had already described a Discoplea 

 Rotula, and also a Disc. Rota, both from the South Seas, 

 which Kiitzing afterwards supposed to be also species of 

 Cyclotella, he, in his Species Algarum, changed his former 

 appellation from C. Rotula to C. Astrcea. This change was 

 uncalled for, as the first diatom described under the com- 

 bined names of Cyclotella Rotida is that of Kiitzing, and 

 that name has been adopted by Smith; to it the name 

 Rotula ought still to be attached, unless we take into con- 



* Catalogues of names are of very little use when not accompanied with 

 diagnostics! remarks taken from the specimens collected ; for if the writer 

 makes a mistake, as all may readily do in microscopical objects, there is no 

 way of ascertaining what was intended. 



VOL. VIII. U 



