KEPORT ON THE DIATOMACE^E. 25 



The specific name has reference to the occurrence of this frustule in the frozen 

 Antarctic Ocean. 



Plate XXVII. fig. 9, probably represents a variety of this species differing from 

 the typical form in the following respects — (1.) the dimensions are much greater, (2.) 

 the appearance is more swollen, and (3.) the striae are relatively much finer. The arrange- 

 ment of these striae and the character of the stauros show its close affinity with Stauroneis 

 glacialis, n. sp. ; nevertheless, apart from its sublanceolate profile, its true varietal or 

 specific character must at present remain somewhat doubtful. 



Stauroneis pygmea, n. sp. (Plate XXIX. fig. 7.) 



Parva, elongata-elliptica ; apicibus rotundatis ; area transversa sublineari marginem 

 non attingente ; striis moniliformibus subradiantibus. In mari Arafura. 



This small form from the Arafura Sea possesses an elliptical outline and rounded ex- 

 tremities. The raphe is somewhat bent, and the stauros terminates in an irregular manner 

 at a notable distance from the edge of the valve. The striae are moniliform and radiat- 

 ing, and near the middle line they form a well-marked double somewhat irregular area. 



Pinnularia, Ehrenb. 



Nomenclature being nothing more than a means employed to facilitate the work of 

 the naturalist in the description of the innumerable organic types with which he has to 

 deal, Ehrenberg wisely divided the genus Navicula, Bory, which was already extremely 

 rich in species, into two, and included under the generic name of Pinnularia those 

 naviculoid forms whose valves were ornamented with pinnulse or costae and not by rows 

 of granules. It is true, indeed, that some refuse to admit this distinction on the ground 

 that the sculpturing of all naviculoid forms is ultimately reducible to granules, but, 

 although some species, such as Pinnularia peregrina, Ehrenb., have been attributed to 

 the genus Navicula because of the recognition of longitudinal lines which are made up 

 of a dense series of oblong granules, all similar forms are not really granulated, there being 

 many Pinnularice, which, when observed with the best object-glasses, with the most 

 accurate manipulation of the light, and by the use of monochromatic illumination, have 

 exhibited no granular structure. 



Pinnularia raeana, n. sp. (Plate XV. fig. 3.) 



Lanceolata ; valvis spiraliter inflexis ; linea media sigmoidea in area laevi lanceolata ; 

 costis circum radiantibus. Ad Zebu, ex insulis Philippinis. 



This very singular and elegant species was discovered by Dr Eae in a collection 

 brought from Zebu in the Philippine Islands. It possesses a very graceful lanceolate 

 form. The central line or raphe is slightly sigmoid. The radiating continuous costse do 



(bot. chall. exp. — part iv. — 1886.) D 4 



