KITTON, ON NEW GENERA AND SPECIES, 119 
be merged into one genus containing some four or five 
species. 
Another instance of a supposed new species proving to be 
otherwise may be mentioned, viz. Actinocyclus triradiatus ; 
this the author afterwards found to be only a secondary plate 
of Actinocyclus undulatus, Sm., <Actinoptychus senarius of 
Ehr. (By some unaccountable oversight of Professor Smith’s, 
he has confounded Ehrenberg’s Actinocyclus with his Acti- 
noptychus.) The genus Actmoptychus, Ehr., contains the 
form with undulate valves, like the Actinocyclus undulatus, 
Sm. Actinocyclus, Ehr., contains the discs with radiating 
series of granules, and a pseudo-nodule, like Smith’s Eupo- 
discus Ralfsii, sparsus, &c.) 
A similar case occurred to myself. A friend sent me a 
slide of the so-called Bermuda earth (a Miocene deposit 
from Bermuda Hundred, New Nottingham, U.S.), in which 
he had marked a new species of Heliopelta; this I found on 
examination to be a secondary plate of Heliopelta Met. It 
does not appear to be generally known that the valves of many 
species of Diatomaceze are composed of thin, siliceous plates, in 
some cases similar, in others dissimilar. In Heliopelta the 
secondary plate is finely striate, similar to a Pleurosigma; in 
Actinoptychus undulatus it is irregularly punctate. The 
valves of Actinocyclus( Actinoptychus) triangulatus, Brightwell, 
in the ‘ Jour. Mie. Sci.,’ Vol. VIII, Pl. V, fig. 2, will some- 
times separate into three similar plates or lacune ; the draw- 
ings 2a and 2b, are not intended, as there stated, to represent 
a frustule undergoing subdivision, but the plates in sitd. ‘The 
same phenomenon occurs in the valves of Actinocyclus Ralfsii ; 
the secondary plates are hyaline, and marked with very faint 
radiating granules, like faint impressions of the primary plate. 
I adduce these examples as illustrating the danger of institut- 
ing new genera and species from observations made on single 
specimens, and these, perhaps, from fossil deposits or dredg- 
ings. No new species should be published until a copious 
gathering has been obtained, and the form studied in a living 
state if possible. 
Habitat has also much to do with the appearance of the 
diatom. A species in an unfavorable locality will not 
secrete the same amount of silex as the same species in a 
more favorable locality ; the markings are much fainter, and 
the valves thinner; self division goes on, and every new- 
formed frustule is less strongly developed than its predecessor, 
and thus a gathering appears to contain several new species. 
Again, an abnormal frustule may be formed, and if self- 
division occurs the departure from the original will be 
