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



Fragilaria linearis, n. sp. (Plate XIX. fig. 9.) 



E maximis ; valvis linearibus, transverse striatis, apicibus rotundatis. la mari 

 Antarctico. 



This Diatom was collected in the Antarctic Ocean. The form of the valve is not 

 "linear-lanceolate or fusiform," but is absolutely linear, and provided with rounded 

 extremities, so that in this respect it differs from that of any previously recorded species 

 of the genus. Hence Pritchard's definition, 1 as given in his History of Infusoria (p. 776), 

 must be extended, there being no doubt as to the fact that this frustule belongs to the 

 present genus. The generic description may be amended as follows : — " Frustules linear, 

 united into a filament, lateral valves smooth or faintly striated, linear, liuear-lanceolate 

 or fusiform." 



Fragilaria antarctica, n. sp. (Plate XXV. fig. 12.) 



Frustulis seriatim dispositis ; valvis plus minus subcurvatis, transverse raro plicatis ; 

 inter plicas duplex punctulorum ordo ; punctula invicem alternantur. In mari Antarctico 

 passim. 



The two valves shown in the present figure are of very different sizes, yet the identity 

 of their structure indicates that they belong to the same genus, although in the larger 

 specimen the want of symmetry along the longitudinal axis is more pronounced than in 

 the other. This want of symmetry is not found in other forms of Fragilaria, except in 

 the case of Fragilaria (?) pacifica, 2 Grun., which is figured in the Synopsis des Diatomees 

 de Belgique, Plate xliv. figs. 20-22, and of Fragilaria (?) schwarzii, Grun., represented 

 at fig. 24 of the same plate. With these two examples before us, however, the present 

 frustules may be classed as FragilaricB, especially as the valves are striated by un- 

 interrupted rows of points — a character which is generally found in the Fragilaria'. 

 Strictly speaking, however, this t)-pe should not be placed among the Pseudoraphidieae, 

 but among the Cryptoraphiiedse. 



The structure of the valves is very characteristic. ' The surface is traversed trans- 

 versely by thinly-set but deep folds, so that the intervals resemble large granules when 

 viewed from the zonal side. Between the folds or plicae there are two lines of sparsely 

 disposed punctiform granules, which alternate with one another. The Diatom is very 

 common, and is quite characteristic of all the collections from the Antarctic, being found 

 sometimes isolated and sometimes in series. When in series the frustules are not linear, 

 but somewhat inflated, owing to the convexity of their outline. 



1 This definition is as follows : " Frustules linear, united into a filament ; lateral valves smooth or faintly- 

 striated, linear-lanceolate or fusiform." 



2 The localities given for Fragilaria (?) pacijica, Grun., are " Cap. de Bonne-Esperance et lies Samoa," and 

 for Fragilaria (?) schwarzii, Grun., " lies Seychelles." 



