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



Since Rabenhorst 1 constituted a variety b for a form with obtuse apices, the present 

 frustule has been indicated as variety c on account of the acuteness of its extremities. 



Stauroneis brebissonii, n. sp. (Plate XV. fig. 4.) 



Oblonga, medio late constricta ; apicibus cuneato-obtusis, subproductis ; striis ad 

 nodulos radiantibus et medio aream laavem linquentibus. 



This is one of the most curious forms of the genus Stauroneis. The valve is of oblong 

 form, being narrower in the middle than at its extremities, and the two longitudinal lines 

 are slightly sigmoid. The extremities are cuneato-obtuse and exhibit a slight constriction. 

 The striae are strongly radiating towards the centre and towards the nodules, and they 

 terminate as in Pinnularia divergens, 2 W. Sm. They are absent in the centre of the 

 valve, so that this area is very wide and is bounded only by the nearest striae. The zonal 

 side is sub-rectangular. 



This species is named in honour of one of the earliest naturalists who prosecuted the 

 study of Diatoms, Alphonse de Brebisson. 



Stauroneis oblonga, Bail. (Plate XX. figs. 7 and 11.) 



Different sizes of this species are here represented. On comparing the figures with 

 Plate xlviii., fig. 16, of A. Schmidt's Atlas, one cannot fail to recognise the justice of the 

 determination here arrived at, although the definition of the species, which is given by 

 Pritchard, 3 does not at all agree with the present figures, which are of the form called 

 " linear " by Bailey. 



In this species it may often be observed that the striae on one side touch the raphe, 

 whilst on the other they stop short of it. This, however, cannot be compared with what 

 takes place in Alloioneis, but is to be attributed to the fact that the raphe is raised and 

 forms an oblique projection on one-half of the valve. 



Stauroneis glacialis, n. sp. (Plate XXVII. fig. 11.) 



Magna ; valvis longitudinaliter late convexis, transverse arete convexis ; stauro lineari ; 

 striis dense transversis parallelis. In mari Antarctico. 



This curious navicular frustule was collected in the Antarctic Ocean. It is of large 

 size, and its valve is very convex in a longitudinal direction but much more so in a 

 transverse, so that it cannot be entirely brought into focus at the same time. A median 

 stauros stretches in a linear manner between the raphe and the margins. The striae, which 

 are very fine, are directed transversely. 



1 Eabenhorst, Flora Europsea Algarum Aquse dulcis et submarina?, p. 251. Hero variety b is characterised as 

 follows : "Forma sub polis leniter constricta, apicibus obtusis." 



2 Synopsis of the British Diatomaceae, vol. i. p. 57, pi. xviii. fig. 177. 



3 This definition runs as follows : " Linear, with acute, cuneate ends, and oblique punctato-asperate striae ; 

 stauros abbreviated, dilated outwards. . . . The size and markings of Staurojitera aspera, Ehrenb., but having 

 its valves oblong, with parallel sides, and acute angular ends." — History of Infusoria, 4th edit. p. 914. 



