310 MEMORANDA. 



Avhich it seems connected ; sometimes it is curved ; but whether 

 both structures occur in the same species, or are indicative of 

 different species, no evidence has hitherto been adduced. 

 Smith's figures 152a*, 154a, and 274a, may be taken as 

 examples of the one, and 152a, 153a, and particularly 153a 

 and 154a*, of the other. The striae appear, however, to pre- 

 serve nearly the same inclination to the new or intermediate 

 lines which they did in the non-sporangial state to the median 

 line; and hence the direction of the striae is not sufficient of 

 itself to distinguish species, however good a character it may 

 afford, unless regard be had to the peculiar state of the frustule. 



Perliaps I may be allowed here to remark that from the 

 days of Linnaeus it has been a maxim, although specimens be 

 distributed or figures given with names, such names are held 

 to be unpublished unless clear and precise specific and generic 

 characters be given along with them ; and that he who gives 

 such characters is not bound, except through courtesy, to 

 adopt or refer to the names attached to new figures. The 

 reason is obvious ; specimens or figures only exhibit one form 

 of the species, and afford no information as to its limits, and 

 consequently the same author may, from ignorance of the laws 

 on which species are to be founded, give representations of 

 several forms of the same species ; such names, if all the 

 forms were specifically distinct, may be good, but bad when 

 they are to be united ; the describer or naturalist must, there- 

 fore, not be hampered by the errors of the artist or microsco- 

 pist who preceded him. In Ehrenberg's Mikrogeologia, the 

 most unphilosophical work ever published on Diatomaceae, 

 not one species, although supposed new, is charactei'ized ; and 

 unless one has samples of the same deposit he has depicted, 

 it is quite impossible to guess with any degree of certainty 

 what he intends, unless in some very rare instances. His 

 Biblarium glans is readily seen, no doubt, to be the well- 

 known Tetracyclus lacustris, of which Ehrenberg appears 

 ignorant, and his Synedi'a ? hemicyelus to be Eunotia falx of 

 Gregory, but few others can be so readily made out. In this 

 respect Kiitzing's works have an advantage over Ehrenberg's ; 

 but in many cases Kiitzing merely derives his specific cha- 

 racter from Ehrenberg's figures and not from the diatoin 

 itself, thus adding to the confusion. In the same way in your 

 Journal are several papers by Dr. Gregory, accompanied with 

 figures, but as no specific characters are assigned the figures 

 lose their value, as no one is bound to adopt the names there 

 given. 



In characterizing species a great mistake has crept in of 

 late years not only as to diatoms, but as to flowering plants ; 



