''\4'\ 1'. T. OLEVE, SYNOPSIS OF THE NAVICULOID DIATOMS. 



"c'.,'''' 'In carrying out this work I have been kindly assisted by several diatomists, who sent me 

 fcfe' 'examination slides from tlieir collections. Among them I name with recognition Prof. J. Brun, 

 ;^Ir:KiNKER, Mr. Le-Tourneur, Mr. J. D. Moi^ler, Mr. P. Petit, Dr. Rae, Mr. Thum, Mr. E. Weissflog, 

 WrnL Van Heurck and Mr. Ward. 1 am indebted to Mr. Julien Deby, who sent from his gigantic 

 collection everything of interest to me, and to Mr. E. Grove, who not only sent me a large num- 

 ber of slides, but also took the trouble of revising the manuscript and the proofs. Materials from 

 diiferent parts of the world have been sent by Dr. Aurivillius (from Java), Mr. Beddome (from 

 Tasmania), Mr. DusiiiN (from Cameroon), Captain G. C. Eckman (marine mud from the Atlantic and 

 Mediterranean), Prof. Lagerheim (from Ecuador) and Dr. Norstedt (from Australia, New Zealand 

 etc.). To Mr. Comber I am indebted for many line photographs of several forms of interesting struc- 

 ture. To all these gentlemen I give my best thanks. 



On the value of the characteristics. 



It may be stated as an axiom that those characteristics are of the greatest importance which 

 occur in the greatest number of forms, and on the other hand that the characteristics which occur 

 in some, but not in all, of a number of forms otherwise nearly related are of less importance. The 

 older authors as a rule attached but little importance to the more constant characteristics, but on 

 the contrary gave much attention to trifling differences, because the latter are frequently more 

 conspicuous than the former. They founded not only species but genera and divisions on charac- 

 teristics, which were actually subject to variation in species otherwise identical. I will in the 

 following pages treat of all characteristics which have been used for the description of species and 

 genera. 



Hahit of life and (/rowfh. Most diatoms live in a free state, floating in the water, but many 

 are attached to solid bodies in the water, some are stipitate on gelatinous stalks, and, others enclosed 

 in gelatinous tubes or masses of different shape and consistence. A careful examination shews that 

 many of the attached or enclosed forms also occur in a free state; and that there are frequently 

 very slight differences between species, which live attached or enclosed, and others which never 

 occur in such a state. On the other hand forms, which are stipitate, or enclosed in tubes, belong 

 to the most different types. For these reasons I regard as a characteristic of very little im- 

 portance tlie mode of occurrence in free or attached state. At least, genera and species should 

 not be founded on such characteristics alone. Genera, such as Schisonema, Endostaaron, Endosigma, 

 Encynnema, Cocconema, are in my opinion not acceptable. ^ 



Size. The limits of the dimensions of the forms of each species are in most cases pretty 

 definite, the larger forms of each species being as a rule twice as large as the smallest. Still, in 

 some cases the variabilitj^ is more extensive and the followings may be cited as species in which 

 the dimensions of the forms are subject to very considerable variation: Amphora ovalis, Achnanthes 

 brevipes, Pinnularia viridis. 



Form of the frus/ule. Most frustules of the Eaphidiete are straight, and nearly symmetrical, 

 with the longitudinal and transverse axes, but a great number of forms are in some or other 

 respects asymmetrical. A flexure of the frustule along the longitudiiial, or the transverse axis, 

 occur in the old genera Cocconeis and Achnanthes which have been distinguished hitherto principally 

 by this characteristic. As to Cocconeis it seems probable that the flexure may be derived from the 



' The gelatinous substance ol' the stipes ol' Achnanfes longipes is intensely stained by hwmatuxyline, and nu eon- 

 tinnation of the substance of the stipes is visible in (he interior of the frustule. On the other hand the stipes is not stained 

 by (/ongo-red, methyle-green, eosine, and niethylene-blue. The gelatinous tubes of Navicula (Schizonenia) mollis are stained 

 by hffimatoxyline, fuchsine, methyle-green and saffranine, but not by eosine. The tubes of Amphipleura (Berkelya) Dillwynii 

 are stained by hasmatoxyline and methyle-green. but not by Congo-red. The gelatinous eiivelopes of Mastologia are stained 

 by methyle-green, fuchsine and saffranine. but not by eosine and Congo-red. 



