ATLAS DER DIATOMACEENKUNDE. 27 



given as distinct species (many of them new), the remainder repre- 

 sent " critical forms " and varieties. 



Plates 19 and 20 contain the following forms of Surirella, viz., 

 five varieties of S.fastuosa, S. recedens, S. intercedens, S. Collare, 

 S. sentis — a very fine and remarkable form the ridges of the cana- 

 liculi are distinctly spinons. S.Jausta (the sp. name of australis, 

 PL iv., fig. 20, to be deleted) ; this species is probably only a 

 variety of S. lata. S. deflexa, distinguished by the sigmoid out- 

 line of the median space ; S. lepida resembles S. striatula, S. 

 anfractuosa, S. arabica, S. Baldjikii. The above forms belong to 

 the fastuosa type. S. Giiindleri — this, the author thinks may be 

 only a variety of S. pidchra, S. Fehigerii, S. inducta, and >S^. 

 Kurzii. 



In the five parts now issued we find 64 figures of Surirella ; 19 

 of these represent forms of S. fastuosa. I am inclined to think 

 that all forms with a striated border to the median space should 

 be considered as merely variations (not varieties) of S. fastuosa. 

 It is, perhaps, open to doubt whether it is desirable to figure so 

 many forms exhibiting only the minutest differences. If this plan 

 is carried out, this work will contain at least 30,000 figures. The 

 following is a list of the genera already published, with the number 

 of figures illustrating them :^ 



Actinoptychus - - 26 



Campylodiscus - - 123 (not completed). 



Coccouema - - 35 



Cymbella - - - 79 



Encyonema - - - 34 



Navicula - - - 382 (not completed). 



SurireUa - - - 64 (not completed). 



Professor H. L. Smith's list of genera contains about 400 

 names ; allowing for synonyms, &c., we may fairly estimate the 

 number at 300. As the twelve monthly parts represent one-sixth 

 of the entire work, and as the number of figures in the six parts 

 will probably not exceed 1000, the "Atlas," when complete, will 

 contain more than 6,000 figures. It must, however, be remem- 

 bered that the author states in his Prospectus that only those 

 forms which are subject to great variation will be treated in this 

 exhaustive manner. All the figures in the parts just published 

 are remarkably accurate representations of the actual forms. 



Part 5 contains a circular from the author, in which he alludes to 

 the corrected explanatory tables which are to take the place of 

 those now given. To enable him to do this with the accuracy he 

 desires he most respectfully requests all who can afford him 

 assistance in the form of well-founded criticisms, or the correction 

 of any errors in nomenclature, will have the kindness to do so. In 

 conclusion, he remarks, " I venture to say that I make this 



