8 



MARINE AND FISHERIES 



6-7 EDWARD VII., A. 1907 



BACTERIASTRUM. Schadh. 



Tiiia genius is ^ho exquisitely ladapted for its floating life. It is composed ol 

 cylindrical joints like Chsetoceras, but instead of each cell having only four bristles, 

 sixteen may be observed in an end view projecting from the interval between contig- 

 uous cells and bifurcating as they radiate outwards (fig. 13). The species, B. varians, 

 was observed towards the middle of September, the joints measuring 50 x 25/x, the 

 basal part of the bristles 25 v., and the forks 60,;'.. 



SKELETONEMA. — GreV. 



This is another similar form, which, however, appears to depend on the slenderness 

 of its cylinders and the tenuity of its siliceous coat for its floating power. The species 

 observed, which is also recorded from tne North Sea, is S. costatum (fig. 14), portions 

 of the slender cylinders being ribbed. The frustules in the specimens observed mea- 

 sured about 40// in length by 4 in width. 



In addition to the foregoing plankton diatoms, many other of more littoral habit 

 were frequently taken in the tow-nets. Especially is this true of certain forms like 

 Nitscliia clostermm (fig. 18), or N. longissima (fig. 19) whose shape favours flotation, 

 or like Striatella (fig. 15), whose siliceous shells are thin, and specific gravity there- 

 fore small, or like Licmophora (tig. 16a and b) which are frequently found attached to 

 floating or swimming organisms- like Copepoda. But there are again other forms, 

 the shape of whose aggregations adapts them to a floating life; such are Synedra 

 nitscMoides (fig. 22), Nitschia paradoxa (fig. 17), whose cells perform the most remark- 

 able evolutions, Tabellaria (fig. 24), and Rhabdonema (fig. 20). 



PBOTOCOCOIDE^. 

 Trochisia — Kuetzing. 



This genus includes certain unicellular forms with a thick cell-wall generally 

 ornamented with spines or ridge-like projections. 



Tr. Clevei Lemm., or a representative of this species, occurring at the same time 

 which the spines are imbedded (Plate III., fig. 1) ; it was common towards the end of 

 July. The dimensions (the cell 31,', spines 10 /) are somewhat diflerent from those 

 recorded by Lemmermann (No. 5), and the ends of the spines have more than two or 

 three points, but these differences do not appear to have more than varietal signifi- 

 cance. 



Tr. Clevei Lemm., or a representative of this species, ocurring at the same time 

 as the above, agrees on the whole in its dimensions (cell 72 — 93,a, spines 98 — 51//), 

 with Lemmermann's account, but the conformation of the spines is slightly different. 

 There is no gelatinous envelope, the cell-wall is thin and the hyaline spines are often 

 ' flaming ' or divided at the end, and may vary in length and strength (Plate III., fig. 2). 



Tr. dictyon (Joerg.) Lemm. — I find a single example of this species, the cell-wall 

 of which is marked off by ledge-like ridges into quadrangular or pentangular areas, 

 recorded in my sketches in September, 1901 (fig. 4). The cell measures 96 // in trans- 

 verse diameter. 



HEXASTERIAS. Clsve. 



Several examples of the type species of this genus H. prohlematica Cleve (Plate 

 III., fig. 5), occurred towards the end of August, both in 1901 and 1902. It is charac- 

 terized by 6 (or 7) arms projecting from a central disc about 40 ' in diameter. The 

 arms end in sharp recurved teeth. The contents become brown with chloride of zinc, 

 but neither the arms nor the disc show a cellulose reaction. This "form has hitherto 



