496 PROFESSOR GREGORY ON 
that D. minor almost looks like a miniature of D. distans ; but on a close compa- 
rison, they are found to be totally distinct. D. distans often occurs shorter than 
the average length of D. minor, but it never loses its own characters, the strong, 
distant, glassy costze, and the broad S.V. But the two forms are evidently allied 
species, and both seem to be true Denticule. 
37. Denticula staurophora, n. sp. Pl. X., figs. 37, 376, and 37¢c. Form of 
F.V., which occurs in chains of two, three, and sometimes more, rectangular, with 
coarse marginal strize, which in the middle on each side, are interrupted by a 
blank space, bounded by diverging lines. Length from 0-001” to 0:0038” ; breadth 
0:0005” to 0-0008”, the shorter examples being the broadest. S.V. lanceolate, rather 
narrow, marked with coarse moniliform strize, except in the middle, where there 
is a broad stauros, on each side of which is a line, curved and concave towards 
the extremities. Strize 14 to 16 in 0-001”. 
This striking form is not unfrequent either in Lamlash Bay or in Loch Fine. 
I have referred it to Denticula, but perhaps it ought to be referred to Diadesmis, 
or, if the stauros be considered an objection, to a new genus allied to Diadesmis 
as Stauroneis is to Navicula. But this point must be left for farther investi- 
gation. 
38. Denticula fulva, n. sp. Pl. X., figs. 38 and 386. Form of F.V., which oc- 
curs in chains of two, three, and sometimes four, linear, rectangular, and slightly 
expanded at the apices, the margin marked with the ends of somewhat coarse 
strie. Length from 0:0018" to 0-004’; breadth 0:0005". 8S.V. linear, narrow, 
broadest in the middle, and gradually contracting to long, narrow extremities, 
which are ultimately subcapitate and rounded. Strive moniliform, somewhat 
coarse, leaving a raphe in the middle, and the two terminal knobs unstriated. 
No central nodule in the 8.V.; but the two nodules seen at each end of the F.V. 
appear to form the unstriated knobs at each end of the S.V. 
This well-marked species occurs with the three last, and is even more fre- 
quent than they are. The genus cannot be considered as determined with cer- 
tainty. 
39. Denticula marina, n. sp. Pl. X., figs. 39 and 396. Form of F-.V. linear, 
rectangular, with the angles very slightly expanded, and the margin strongly 
denticulate. It occurs in chains of from 2 to 18 or 20, so that the filament 
seems to be tenacious. Length from 0:002’, to 0:008" or 0-009"; breadth from 
00003" to 00005". §.V. linear, expanded at the middle, and obtusely acuminate 
at the ends. Strize very coarse, and very coarsely moniliform, about 10 in 0-001’. 
On each side of the median line each of the strize is formed of only two granules, 
which are distant, and half of a third, which seems to be on the margin. The two 
or three central strive on each side, having only one and a half granules, the inner 
granule of each being absent, there is a blank space round the centre; and there 
is a smaller blank at each apex. The F.V. here figured is of about the usual 
