48 Dr. Gregory, on Post-tertiary Sand of Glenshira. 
20. Pinnularia injlexa, n. sp. This is a remarkably neat 
little form, well marked, and frequent in the lighter densities. 
Form elliptic lanceolate, ends acute. Striation conspicuous. 
Costse subdistant, highly radiate, leaving in the centre a 
rather large round blank space, about 26 in O'OOl". Near 
each apex is a strong black cross-bar across the valve, which 
I believe to be caused by a depression in the valve, and I have 
named it from this character. Length 0*0014 '. It is very uni- 
form in its characters, and is well represented in fig. 20. (276.) 
21. Pinnularia acutiuscula^ n. sp. This is another well- 
marked species, frequent in the finer densities. Form long, 
almost lanceolate, with the sides parallel in the middle, and 
slowly converging to the acute apices. See fig. 21. Length 
from 0 002" to 0*0026 Striae distinct and conspicuous in 
the middle part, from being more widely separated. They 
are also radiate, but less strongly so than those of the two 
preceding forms. They are finer than in these forms, and are 
about 30 in '001". The only form to which this one has any 
resemblance is P. acuta, but its peculiar form and aspect are 
quite sufficient to distinguish it. Both forms occur here, and 
when seen together appear quite different. (277.) 
22. Pinnularia Ergadensis, n. sp. I have given this name, 
from Ergadia, Argyll, to the species represented in fig. 22. 
Form nearly linear, or linear elliptic, ends rounded, obtuse, 
almost truncate. Length from 0*002" to 0 0045", or more. 
Striation finer than in P.fortis, but conspicuous ; costae about 
25 in 0*001", sub-distant, not quite reaching the median line, 
somewhat inclined. It is frequent in the lighter densities, 
and has a perfectly distinct aspect, so that it cannot be con- 
founded even with P.fortis, the form which it most resembles, 
but in which the character of the striation is totally different. 
As yet, I have met with none of the species of Pinnularia 
here figured, except in the Glenshira sand. (278.) 
23. Stauroneis amphioxys, n. sp. This curious form is not un- 
frequent in the lighter densities, and is well represented in fig. 23. 
Form nearly rhombic, tending to lanceolate, with acute 
apices. Valve highly convex, so as very often to pre- 
sent the dark appearance of an air-bubble, and, even in the 
best position, showing the margin as a broad black line. 
Stauras broad, reaching the margin, very transparent, so as 
often to be seen with difficulty, if in the least out of focus. 
At other times it is black, from the general convexity. Striae 
fine, very nearly parallel, transverse, nearly 60 in 0*001", not 
conspicuous, often apparently irregular, from the convexity of 
the valve. (279.) 
{To he continued.) 
