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



Navicula mirabilis, n. sp. (Plate XXX. fig. 10.) 



Rhomboidea-elliptica ; striis binatis moniliformibus radiantibus ter utrinque inter- 

 ruptis ; nodulo centrali subrotundo. Ad Zebu, ad insulas Philippinas. 



This magnificent elliptical form seems at first sight to be identical with Navicula 

 sniithii, 1 Breb., which, on the whole, resembles it in its general characteristics. In the 

 latter, however, each half of the valve is divided into two unequal parts by a single longi- 

 tudinal line, whilst in the present case there are three longitudinal lines on each side of 

 the raphe and cutting the transverse and subradiating granulated striae. Moreover, the 

 shape of the present valve is rhomboido-elliptical rather than elliptical, so that it must be 

 viewed as specifically distinct from Navicula smithii. Navicula mirabilis was obtained 

 at Zebu near the Philippine Islands. 



Navicula cyclophora, n. sp. (Plate XXVIII. fig. 18.) 



Minima, elliptico-subinflata ; apicibus obtuso-rotundatis ; striis radiantibus ; cyclo 

 laterali ad nodulum centralem. In mari Antarctico. 



This form was gathered between Kerguelen and Heard Islands. It is remarkable in 

 having on one side of the central nodule a very small circle, which is not due to any 

 casual superposition, but is a part of the valve itself. A similar phenomenon occurs in 

 Cocconeis cyclophora as made known by Grunow. 2 



In a most interesting collection from Bahia given to me by Mr Weissflog I have 

 observed another species of Cocconeis with a lateral mark, and two years ago in the Gulf 

 of Naples a third form was recorded as possessing the same peculiarity. Hence, instead 

 of being viewed as of specific value, this character may be regarded as being analogous to 

 the craticular condition of some Navicula. This view is confirmed by a micro-photograph 

 of a Navicula lyra, Ehrenb., which has been furnished by Mr Weissflog, inasmuch as the 

 valve, which has its centre marked by small circles, is distinguished by possessing a lateral 

 hyaline area. 



Navicula, sp. (?) (Plate XX fig. 6.) 



In this figure there is delineated a small naviculoid frustule which differs slightly from 

 the preceding in the form, direction, and perhaps also in the fineness of the strise. More- 

 over, instead of the small lateral circle found in Navicula cyclophora, n. sp., it possesses a 

 non-striated space on one side of the central nodule. Both forms, however, agree in 

 having the two sides of the valve unsymmetrical. Its specific value must at present 

 remain uncertain. 



1 See note on this species in Smith's Synopsis of the British Diatomacese, vol. ii. p. 92 ; Pritchard, loc. cit. 

 p/898. 



2 Dr. H. van Heurck, Synopsis des Diatomees de Belgiquc, pi. xxx. figs.^24 and 25. 



