Development of Trachyneis aspera Gleve. By T. Comber. 403 
observers. They bad a costate structure, and were therefore properly 
referable to the genus Pinnularia ; but in all other respects they 
were undistinguishable from other forms, which had what were termed 
moniliform striae. Thus Prof. Gregory, in his paper on the diatoms 
found in Glenshira Sand, published in 1856, described a costate 
form (his fig. 15) as having “ Every appearance of being a variety of 
N. didyma (agreeing precisely, as it does, in form and size with the 
commonest small form of that species, which is very abundant in 
the deposit), and if that be so, we have moniliform and costate striae 
in the same species.” 
In the same paper he figures, as N. nitida, another simply costate 
form, which Prof. Cleve refers, I believe rightly, to his Diploneis 
Crabro, a species which normally has its costae “alternating with 
double rows of alveoli.” 
Yet another instance is the form called by O’Meara Pinnularia 
arraniensis. He describes it as having “ Striae coarse . . . distinctly 
costate ” ; but it is now referred by Prof. Cleve to Diploneis nitescens, 
which ordinarily has its costae alternating with rows of alveoli. 
Again, Prof. Cleve considers Navicula Doczyi, Pantoczek, to be 
“ a finely costate variety of D. Smithii.” Its costae are described as 
only “ indistinctly punctate ” ; whereas in D. Smithii the costae are 
“alternating with double rows of alveoli.” 
Is it not possible that, in each of these cases, the forms with 
simple costae may be the immature stages of the others ? If they 
ever occur pure this cannot be the case ; but such of them as I 
have met with have always been in company with the forms of more 
complex structure ; e. g. N. nitida is always associated with D. Crabro , 
and may well be regarded as merely an immature state of that species, 
in which the intercostal alveoli have not yet developed sufficiently to 
be conspicuous. 
In other sections of the genus Navicula , what appear to be, in 
like manner, costate forms of species normally punctate or granulate, 
occasionally occur. Thus Pinnularia divaricata , O’Meara, is described 
as having costae that in some aspects “ appear as if they were slightly 
notched by longitudinal lines which, though they produce a furrow, do 
not sink so deeply as to give a moniliform character to the sculpture 
of the valve.” It is now commonly referred to Navicula latissima , a 
species having striae conspicuously punctate. 
I have also a specimen in every respect like Navicula angelorum, 
Cleve, except that its structure is much less conspicuously punctate. 
Further observation is, however, required to determine whether 
the suggestions made regarding these other species can be accepted 
or not. They are at present advanced merely as suggestions, whereas 
the immature costate condition of Trachyneis aspera is an observed 
fact. 
