478 PROFESSOR GREGORY ON 
2. Navicula Cluthensis,* n.sp. Pl. IX., fig. 2. Form oval, rather broad. Me- 
dian line broader at the centre, narrower at the apices. Central nodule definite, 
large; terminal nodules smaller. Length 0:0013" to 0:0016"; breadth about 
0.001”. Strize conspicuous, clear, and sharp, inclined slightly in the middle, 
strongly near the ends ; about 20 in 0:001”, 
Fig. 2 represents this form, which occurs in Professor ALLMAN’s dredging from 
Lamlash Bay, and though not abundant, is yet frequent enough for all practical 
purposes. It is very uniform in its characters, and though the description above 
given may not appear very characteristic, yet I know of no form with which this 
one can be confounded. Its aspect is so peculiar that it is instantly recognised. 
3. Navicula (?) inconspicua, n. sp. Pl. IX., fig. 3. Form linear, rather narrow, 
with rounded ends. Median line strong, complex, interrupted in the middle. 
Nodule definite. Aspect of valve hyaline. Striation so fine that it has not yet 
been resolved; and at all events it cannot be visible under a power of 400. 
Length 0-002” to 0:0032; breadth about 0-00035.” 
This little form occurs both in Lamlash Bay and in Loch Fine. I do not feel 
quite sure that it is a Navicula, as it may possibly belong to a filamentous species ; 
it may be, for example, a Diadesmis; or it may prove to be a Schizonema. This 
can only be ascertained by observations on examples in the living state. 
4. Navicula brevis, n. sp. PI. IX., fig. 4. Form nearly elliptical in the middle; 
broad, short ; contracted to short, produced, obtuse extremities. Length about 
0:0023"; greatest breadth 0:0013". Strize fine, about 35 in 0-001’; very slightly 
inclined, not reaching the median line, and at the centre leaving a large, round, 
blank spot,within which the two halves of the median line end in small rounded 
expansions. Central nodule indefinite; terminal nodules definite. 
This form is easily recognised by its short, squat shape, and is distinguished 
from NV. semen, which it resembles in form, by its much finer striation. It occurs 
in Lamlash Bay, and is not very scarce in Professor ALLMaAN’s dredging from that 
locality. 
5. Navicula Claviculus,n.sp. P1. IX., figs.5,56, and 5c. Form of valve linear, 
narrow, with one central and two terminal expansions, separated only by two 
constrictions. The terminal expansions are much elongated, oval at the extre- 
mities, and rather broader than the central expansion. Central nodule definite. 
Length 0:0015” to 0-002"; greatest breadth 0:0002” to 0:0003". On the 8.V., 
figs. 5 and 50, the central expansion is unstriated. Strice on the rest of the valve 
transverse, sharp, not quite reaching the median line; about 32 in 0:001”. The 
F.V., fig. 5 ¢, is rectangular, with slightly expanded and bevelled angles, and exhi- 
bits the same absence of strize from the middle part. The strize are seen to a 
* From Clutha, the Clyde. 
+ Figs. 5 b and 6 ¢ are magnified 800 diameters, to bring out the details. Fig, 5 is magnified 
only 400 times, and is below the average size. 
