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



not reach the raphe, but leave a smooth somewhat lanceolate area around the centre of 

 the valve. 



The specific name is given out of respect to its discoverer. 



Pinnularia criophila, n. sp. (Plate XV. fig. 2.) 



Anguste rhomboidea, transverse costata ; costis lineam mediam attingentibus ; 

 apicibus rotundatis ; valvis transverse convexis. Ad mare Antarcticum. 



This form was brought from the glaciers of the Antarctic Ocean. The valve, as may 

 be noted by comparing the figures representing the valval and zonal aspects, is not flat 

 but transversely convex, so that its form somewhat resembles that of the diatom * shown 

 in Plate xlvii. fig. 1 of Dr. A Schmidt's Atlas, although it is at once longer and narrower 

 than the latter, which, moreover, is not transversely convex. It is rhomboidal in general 

 outline, transversely costate — the costse reaching the median line — and its apices are 

 rounded. 



Pinnularia sp. ? (Plate XV. fig. 1.) 



We have here represented a bilobate form in which the stria? are continuous. The 

 frustule is elegant in general appearance, elongated in shape, and provided with a wide 

 central contraction. The two lobes into which it is thus divided are elliptical. The 

 radiately disposed lateral costae are interrupted by two wide longitudinal bands. Between 

 these and the median raphe there is a long sublinear and elliptical area on which, towards 

 the middle line, the terminations of the costse may be traced. The central nodule is 

 oval, its long axis being directed transversely. The fact that navicular bilobate frustules 

 are apt to present a difference of structure according to the stage of development at w T hich 

 they have arrived renders it difficult to decide on the true taxonomic value of this type, 

 hence it has been provisionally recorded as an undetermined species of Pinnularia. 



Navicula, Bory. 



The examination of the navicular forms in the Challenger collections has been the 

 means of still further augmenting this already extensive genus. In Pritchard's History 

 of the Infusoria 303 species have been described, in A.. Schmidt's Atlas of the Diato- 

 macese — a publication which unfortunately was interrupted — more than 200 forms are 

 figured, while in Habirshaw's Catalogue of the Diatom acete a still greater number 

 of specific names have been registered. It is true, indeed, that in both of these 

 lists forms possessing continuous striaj, upon which characteristic Ehrenberg con- 



1 "With respect to this frustule Schmidt says : " 1. G. v. Mexico, 2. Spitzbergen, 3. St. George's River, 

 4. Yokohama, Formen, welche weder mit N. (i.e., Navicula) directa noch mit A. loiuja verbunden werden kbn- 

 nen. "—Loc. cit., Explanation of Plate xlvii. 



