58 THE VOYAGE OF H.M.S. CHALLENGER. 



seaweeds on a rock called St Clement's near the port of Ancona, and which was also 

 abundantly represented in a collection of Diatoms from the aquarium of the Zoological 

 Station at Naples. This organism might easily be confounded at first sight with 

 Diatoma hyalinum, 1 Kg. ; but a careful examination of the former reveals the fact 

 that the markings are more frequent on the zonal side, and that in the middle of one of 

 the longitudinal lines an appearance resembling the letter C is presented. The frustules, as 

 iu all Tabellarice, are united in a zig-zag series, and it is exceptional to see one frustule 

 by the side of another or lying isolated. They are connected with each other by means of 

 small membranous cushions generally placed at the angles. In the longitudinal series 

 the position of these points of union alternates from right to left, but in the lateral series 

 they are on the same side in all. Hence in this genus, as in Cocconeis and Achnanthes, 

 the valves are dissimilar to one another, the loculus of one being round. 



The genus Cyclophora may accordingly be defined as follows : — Frustula tabulata, 

 rectangula, in fascias conjuncta, rarius soluta ; isthmo gelineo alterne concatenata ; a 

 fronte linearia vel parum inflata ; valvis inasqualibus, quarum una loculo centrali 

 instructa. 



This genus, of which Cyclophora tenuis, Cstr., is the typical species, has been accepted 

 by all micrographers. Prof. H. L. Smith has recognised it in a recent collection made in 

 America, and Grunow, in the Synopsis des Diatomees de Belgique, has given on Plate 

 xxxvi. figures of Cyclophora tenuis, Cstr., and of a variety — Cyclophora tenuis, Cstr., var. 

 tropica — which was collected in the vicinity of Honduras, the Barbados, and the Isle of 

 France. 



In a note annexed to his table Grunow 2 remarks that in addition to the lonp-itudinal 

 lines, the valves show very fine transverse liues and two terminal nodules ; but it is to 

 be noted that the longitudinal lines, at least, are only on the zonal side. If these two 

 characteristics really exist the definition should be modified, and the existence of the two 

 terminal nodules would render the systematic position of the genus very problematical. 

 On the valves I have hitherto been able to distinguish nothing except the loculus and a 

 slight central line on one of the valves. 



Cyclophora tenuis, Cstr., var. nov. (Plate XXV. fig. 3.) 



We have here delineated two frustules from the Philippine Islands, which were 

 united together and evidently belong to the same genus. These frustules resemble 

 in their profile the figure of Cyclophora tenuis given by Grunow, but do not agree 



1 Kiitz., Lac, p. 47, pi. xvii. fig. 20; Smith, Synopsis of the British Diatomacese, vol. ii. p. 41, pi. xli. fig. 

 312; Pritchard, op. cit., p. 778, pi. iv. fig. 16. 



2 The original note is as follows : " Les valves ont des lignes ru^dianes et des nodules terminaux bien 

 marques. Ces derniers sont un peu eloignds des extremity qui sont obtuses. Les striae transversales depassent 

 le nombre de 30 en - 01 mill. Les lignes longitudinales sont dedicates et un peu ondulees." 



