REPORT ON THE DTATOMACE.E. 41 



Achnanthes kerguelenensis, n. sp. (Plate XX. fig. 15.) 



Valvis lanceolato-rhombicis ; apicibas obtusis rotundatis; striis moniliforrnibus sub- 

 radiantibus. Ail insulam KergueleD. 



This frustule has a lanceolate-rhomboidal outline, thus agreeing with Achnanthes 

 rhoniboides * of Ehrenberg, but instead of possessing acute extremities like the latter 

 it has absolutely rounded and obtuse apices. 



It was found in a sounding taken near Kerguelen Island. 



Achnanthes parallela, n. sp. (Plate XIX. fig. 11.) 



Valvis linearibus ; apicibus rotundatis ; punctulorum liueis subr adiantibus. In portu 

 Thaiti. 



This frustule was found in sand which proved to be rich in various forms of Diatoms 

 and which was obtained from a great depth at the port of Tahiti. The valves are bounded 

 peripherally by straight parallel lines, the extremities are rounded, and the lines of puncta 

 are subradiatinsr. 



No hitherto recorded species agrees with this form, whose specific name has reference 

 to its parallel margins. 



TRIBE II.— PSEUDORAPHIDIE^:. 

 Gephyria, Arnott. 



This genus, as well as that of Eupleuria, was established by Professor "Walker Arnott, 

 but as it not unfrequently happens that the definitions of new genera when first con- 

 stituted are very imperfect, and as further examination often demonstrates not their 

 generic but only their specific value, the Eupleurice and Gephyrice were subsequently 

 united by Professor H. L. Smith, the peculiarities of their structure not being sufficiently 

 well marked to indicate distinct generic characters. 



In both types the frustules, which are united together, consist of dissimilar valves, and 

 the transversely disposed lines on these are cut by longitudinal lines. The transverse 

 ribs, moreover, are so arranged that the areas included between them on the two sides of 

 the central band alternate (Plate XV. fig. 1 0). Both have arcuate valves, but in the case 

 of Gephyria' 2 the lower valve differs from the upper " in having a smooth circular space at 

 each end," while in Eupleuria 3 the inferior valve has "the costse and strise disappearing 

 below the extremities of the valve," although these structures reach the extremity in the 

 superior. 



1 This form is identical with Achnanthes ventricosa, Kiitz., Baa, p. 76, pi. xx. fig. 7, and with Mono/jramma 

 ventricosa, Ehrenh., Monatsber. d. k. Akad. d. Wiss. Berlin, 1843. 



2 Pritchard, op. cit., p. 809. 3 Quart. Juum. Micr. Sci., vol. vi. p. 89. 

 (bot. chall. exp. — part iv. — 1886.) D 6 



