Descriptions of Diatomace^e, chiefly of those found in 

 " Elide " (Lower California) Guano. By Christopher 

 Johnston, M.D., of Baltimore, U.S. 



I am fully aware of the fallacies which beset the dia- 

 tomist who establishes new species from the inspection of 

 rare, isolated, and prepared valves ; but I am of opinion that 

 science is made the gainer by his efforts, provided he is care- 

 ful not to substitute names for things, and fancy for the sense. 

 If the observer states the circumstances under which he 

 obtained his facts, it is certainly pardonable in him to group 

 these together in such a manner as to guide others in extend- 

 ing the limits of knowledge, whether by verifying his speci- 

 fication, or by modifying it, when accumulated observations 

 justify the emendation. 



Species have, doubtless, been disadvantageously multiplied ; 

 but it must be allowed that this error has not unfrequently 

 been innocently committed, either when descriptions in sys- 

 tematic works failed to identify supposed novelties, or the 

 published figures evidenced no correspondence with them. 

 Accurate figures are, unquestionably, of great service in 

 many respects, for they are duplicates, so to speak, of the 

 original specimen ; and " if they fail in some cases to esta- 

 blish species, they will, at least, assist to indicate the range 

 of variation, a point in itself of no small importance." In- 

 deed, it may be said that exactness in description and 

 delineation must largely contribute towards lessening the 

 useless load of nomenclature with which science is charged. 



The source whence the specimens here noticed were de- 

 rived was Californian guano, from the Island of Elide, on 

 the coast of Lower California (lat. 29° N.) ; Patagonian 

 guano; and the stomachal contents of oysters from Ponga- 

 teague Creek, on the Chesapeake side of the eastern shore of 

 Virginia. 



Spatangidum, Be Brebisson. 



It would seem fo be a superfluous task to recur to this 

 "noble diatom" with a knowledge of Greville's delightful 

 paper on Diatomacese which appeared in the April number 

 of this Journal. But I have thought it not unprofitable to 

 add to that author's description of a single valve my own 

 observation of the appearance presented when both are 

 attached, for the character thus afforded is remarkable. 



In isolating specimens preparatory to mounting in the dry 



