REPORT ON THE DIATOMACEiE. 31 



This species, which was obtained from the bottom of the Pacific Ocean, possesses a 

 lanceolate-subrhomboidal outline with wedge-shaped extremities. The surface is covered 

 with dense transverse and subradiating rows of granules that touch the middle line which 

 is interrupted at the centre. 



The specific name has reference to its subrhomboidal outline. 



Navicula oxeia, n. sp. (Plate XX. fig. 8.) 



Parva, lanceolata ; apicibus acutis ; striis transversis, lineam mediam attingentibus. 

 Ad mare Japonicum. 



This small navicular lanceolate frustule was gathered in the Sea of Japan. Its 

 extremities are notably acute, and its fine transverse striae touch the median raphe. 



These characters correspond with those of the type represented in Schmidt's Atlas, 

 Plate xlix. fig. 17, which was obtained from Samoa, and of which the accurate deter- 

 mination was left in doubt. On the other hand, the frustules delineated in figs. 15, 16 

 and 18 of the same plate evidently belong to a different species, and it is by no means 

 easy to understand the grounds upon which Schmidt grouped the four forms together. 1 



The Samoan frustule, as well as that now recorded from the Sea of Japan, may be 

 designated Navicula oxeia on account of the singularly acute character of the extremities. 



Navicula zanzibarica, Grev., var. zebuana, nov. (Plate XXVIII. fig. 8.) 



The present specimen does not fully coincide with the Navicula zanzibarica of Greville. 

 On making an accurate comparison with the figure given by Greville, 2 as well as with 

 that found in Schmidt's Atlas (Plate ii. fig. 3), it may be observed that, while in Greville's 

 species the striae are divided into two series by a smooth longitudinal band, in the present 

 frustule an indication of the striae can be recognised between the band and the raphe by 

 the presence of some minute granules. Moreover, in the latter the two spots, one of 

 which occurs on each side of the central nodule, are tolerably regular, and show in the 

 centre a lineal band formed by stronger granules, but in the former the bands are curved 

 in order to adapt themselves to the form of the granulated side of the valve. The present 

 frustule may accordingly be regarded as a variety, and named, from its origin, zebuana. 



Navicula parallela, n. sp. (Plate XXVIII. fig. 12.) 



Valvis lineariter elongatis ; apicibus cuneato-rotundatis ; striis tenuissimis, parallelis, 

 transversis ; areola laevi ad centrum. In portu Thaiti. 



1 In his explanation of the plate Schmidt explains his figures as follows : — 



" 15. Pudasjarri, 17. Norrland, N. (i.e., Navicula) bisulcata, Lagerstedt. 

 16. Sing-Sing, Hudson R., N.firma var. subundulata, Grun. 

 18. Sodanskylae, nach Grunow Mittelform zwischen N. firma u. N. bisulcata." 



2 Trans. Micros. Soc, vol. xiv., 1866, pi. xii. fig. 22. 



