70 THE NATURAL HISTORY OF THE BRITISH DIATOMACE^. 



mode of development, and method of collecting. The second 

 division, or synoptical portion, will give an accurate and succinct 

 description of all known British genera and species with their 

 synonyms. 



The synoptical portion is to be completed first. The first part 

 commences with the Naviculeae, which, the author says " are by far 

 the most numerous family of the Diatomaceae, of which they are 

 typical, both in the structure of the frustule and the peculiar power 

 of motion they display. . . . Two distinct and well marked 

 types of form or development are met with amongst the Naviculeae ; 

 in the first the valve is depressed or flattened, broad or short (in 

 proportion to its width), the convexity behig slight and confined to 

 near the margin. In the second the valve is elevated or convex 

 and narrow (in proportion to its length), the convexity being great 

 and extending from the margin to the medium line, where it is 

 most prominent. 



" In reconstructing this genus and rearranging its numerous 

 species I have adopted these two types as the basis of classification." 



The author follows Kutzing and other diatomists in combining 

 Navicula and Pinnularia, and he also refers several species of 

 Stauroneis to the genus Navicula, and he is probably right in so 

 doing. 



He retains Professor Smith's term " side view" (S.V.), but 

 abolishes "front view" (F.V.), and substitutes M.V., signifying 

 the view of the frustule exhibiting the median connecting zone and 

 the margin of the valves. This change appears to us to be un- 

 necessary, as the former term was sufficiently intelligible, and has 

 been in use for many years ; if any alteration were desirable on 

 account of simplicity, the letters F and V would be all that are 

 required, the former signify ing the frustular, and the latter the 

 valvular view. 



In the Synopsis of British Diatomaceae, 83 species of Navicula 

 and Pinnularia are described, 60 of which are figured. In the first 

 three parts of the present work 104 species are figured and described, 

 and probably one or two more parts will be required to complete 

 the genus. 



We regret to say that the plates are of very unequal merit — 

 those in Part 2 are particularly unsatisfactory — for example N. 

 cuspidata is represented with much coarser stria? than N. fulva,, 

 although the former is said to have 36, and the latter only 30 

 striae in '001. N. serians is unrecognisable, the wavy longitu- 

 dinal striae, its most characteristic feature, not being shown. 

 (The Author says these longitudinal markings are " plicae or folds 

 on the valve;" this, however, is not the case. The peculiar appear- 

 ance of the longitudinal striae are caused by the granules of which 

 the tranverse striae are composed being placed at irregular intervals, 

 so that the granules in one line of striae are not opposite those above 

 and below it.) A similar arrangement occurs in the large N. rhom- 



