NEW FORMS OF MARINE DIATOMACE.E. 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. Sceptroneis Caduceus, Ehr. PL 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 in such 

 abundance as will probably occur near its true habitat. Ehrenberg thus describes 

 the genus {Bericht der Berlener Akademie, 1844, p. 264), " Animal e Bacillariis 

 Echmelleis, affixum ? Lorica simplex sequaliter bivalvis silicea stiliformis com- 

 pressa, nonconcatenale, cuneata (viva facile pedicellata). Sutura laterum utrus- 

 que valvse longitudinalis media, umbilicus nullus. Habitus Meridii 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 strise. In this fragment we have the 

 large end, which is unusually large, for it is commonly of a narrower 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. Toocarium undulatum, Bail. PL XIV., figs. 107 

 and 107 b. 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. Strise 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. 



