' 
NEW FORMS OF MARINE DIATOMACEZ. 531 
curved. The whole form has a strange appearance, as if we were to take two 
long, narrow stockings, cut them across at the widest part, and join them at the 
cut ends, with the feet pointing opposite ways. From this last character I have 
named it. Length 0-005’ to 0-006’; greatest breadth 0-0006.’ Median line sig- 
moid, straight in the middle, and suddenly bent near the ends in opposite direc- 
tions. Striation so fine that I have not yet succeeded in resolving it, and therefore 
not easily visible under a power of 400 diameters. 
This singular form occurs in the stony Loch Fine gathering so often referred 
to. I have as yet only seen the two specimens here figured, and two more; but I 
have not searched for it, these being so remarkable, and so like each other, as to 
indicate sufficiently, in a general way, the existence of the species. I do not feel 
quite certain as to its genus; but I think it right to direct the attention of ob- 
servers to it. It will probably be found more abundantly in some dredging or 
gathering from a different locality in the Clyde. 
106. Seeptroneis Caduceus, Ehr. PI. XIV., fig. 106. I cannot enter into a 
detailed description of this species, as the fragment here figured is the only spe- 
cimen of it I have yet seen in these dredgings, or in any British gathering. And 
I figure it chiefly as evidence that this genus, which is frequent in several Ameri- 
can fossil deposits, yet lives in our waters, although we have yet to find it insuch 
abundance as will probably occur near its true habitat. Eurensere thus describes 
the genus (Bericht der Berlener Akademie, 1844, p. 264), “ Animal e Bacillariis 
Echmelleis, affixum? Lorica simplex zqualiter bivalvis silicea stiliformis com- 
pressa, nonconcatenale, cuneata (viva facile pedicellata). Sutura laterum utrus- 
que valvze longitudinalis media, umbilicus nullus. Habitus Merzdii non concate- 
nati aut Gomphonematis, umbilico laterali carentis.” 
The species, S. Caduceus, is distinguished by its long slender form, having 
a central expansion, and another at one end, while the other end is long and 
narrow, and by its very coarse moniliform striz. In this fragment we have the 
large end, which is unusually large, for it is commonly of a narruwer and some- 
what elliptical shape. 
This form, which adds one to the list of British genera, occurs in the same 
Loch Fine dredging as the preceding one, and so many more. 
107. Synedra undulata, Greg. Toxariwm undulatum, Bail. Pl. XIV., figs. 107 
and 107 6. Form of frustule very long, and very slender. F.V. rectangular, very 
narrow; S.V. with an elongated central expansion, and two small semi-elliptic 
terminal ones. Margin undulated. Strize conspicuous, moniliform, in the expan- 
sions passing, towards the middle, into an indiscriminate punctation. Length 
0-023"; greatest breadth of S.V. 0:00035" ; breadth of the longer and narrower por- 
tions hardly 0-0001.’ So that the length of the frustule is about 70 times the 
width of the broadest part of the S.V., and more than 200 times that of the greater 
part of the valve. 
