NEW FORMS OF MARINE DIATOMACE^. 529 



101. Navicular.) Libellus, n. sp. PI. XIV., figs. 101, and 101 b. Form of F.V. 

 rectangular, broad, with the angles rounded. The middle part is marked by lon- 

 gitudinal lines or folds, like the leaves of a book ; and when the two halves of the 

 F.V. separate, each retains a broad band of this lineate part. The breadth of 

 the detached halves on the F.V. is so great, that, when united, they must, it 

 would seem, mutually overlap, otherwise the resulting frustule would be much 

 broader than it is. S.V. rhombic or elliptic-lanceolate, broad, with obtuse ends. 

 Length from 0-003" to 0-0035"; breadth of F.V. 0-0017" to 0-002". The S.V. is 

 marked by very fine transverse striae; striae about 60 in 0001"; median line 

 distinct ; nodule definite. When the edge of the S.V. is seen, as in fig. 101 b, 

 the valve seems to be a compound one, formed of five or six, closely packed one 

 over the other. I cannot ascertain if this be so or not. 



This species is frequent in Lamlash Bay, and it much resembles the form 

 figured by me in my second plate from the Glenshira Sand, under the name of 

 N. rhombica, of which also I had figured two of the S.V. in my first plate (T?*ans. 

 Mic. Soc, vol. iv., pi. v., fig. 1, and Mic. Jour., vol. iii., pi. iv., fig. 16). But I 

 observe several uniform points of difference. N. Libellus is more obtuse and broader, 

 and its striation is not only much finer, but the striae are everywhere of uniform 

 size and at a uniform distance ; whereas in N. rhombica, they are near the middle 

 of the valve, not only stronger, but so much more distant than in the rest of the 

 valve as to be almost conspicuous. N. Libellus is also, on the whole, a larger 

 form than N. rhombica. 



But it is very doubtful whether either of them be really a Navicula. They 

 have some resemblance, especially on the F.V., to Schizonema Grevillii, Sm., 

 which, however, is a much smaller form. Still they may possibly belong to 

 Schizonema, but this cannot be ascertained except in living, or at least quite 

 recent and uninjured specimens. The F.V., with its foliated or complex struc- 

 ture, appears to me, however, to differ from that of a Schizonema. 



I may here add, that there occurs in Lamlash Bay a much smaller form of 

 the same shape, but not foliated, at least not distinctly so. This is perhaps the 

 true S. Grevillii. 



102. Nitzschia (?) panduriformis, n. sp. PI. XIV., fig. 102. Form linear, 

 broad, incurved in the middle, acuminate at the ends, which are usually obtuse 

 and rounded, but sometimes acute and sub-apiculate. Length about 0003' ; 

 breadth in the middle 0001" ; at the shoulders 0-0012". The specimen here 

 figured is longer than usual, and the only one I have seen of this length. Margin 

 punctate. There is a faint indication of a double keel in the middle of the valve. 

 Striation fine, both transverse and oblique ; striae about 48 in 0*001". 



This species occurs in several of the Loch Fine dredgings, and is not rare. 

 The striation is similar to that of Tryblionella constricta, Grig. (Mic. Jour., vol. 

 iii., pi. iv., fig. 13) ; but the present form is much larger, and is distinguished 



VOL. XXI. PART IV. 7 C 



