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 00013" to 0*0016"; breadth about 

 0-001". Striae conspicuous, clear, and sharp, inclined slightly in the middle, 

 strongly near the ends ; about 20 in 0001". 



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 002" to 00032; 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. PL IX., fig. 4. Form nearly elliptical in the middle ; 

 broad, short ; contracted to short, produced, obtuse extremities. Length about 

 00023' ; greatest breadth 00013". Striae fine, about 35 in 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 N. semen, which it resembles in form, by its much finer striation. It occurs 

 in Lamlash Bay, and is not very scarce in Professor Allm an' s dredging from that 

 locality. 



5. Navicula Claviculus, n. sp. PL IX., figs. 5, 5 b, and 5 c. 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 0002"; greatest breadth 0-0002" to 0-0003". On the S.V., 

 figs. 5 and 5 b, the central expansion is unstriated. Striae on the rest of the valve 

 transverse, sharp, not quite reaching the median line; about 32 in 0-001". The 

 F. V., fig. 5 c, is rectangular, with slightly expanded and bevelled angles, and exhi- 

 bits the same absence of striae from the middle part.f The striae are seen to a 



* From Clutha, the Clyde. 



f Figs. 5 b and 5 c are magnified 800 diameters, to bring out the details. Fig. 5 is magnified 

 only 400 times, and is below the average size. 



