G8 THE VOYAGE OF H.M.S. CHALLENGER. 



Nitzschia vermiculata, n. sp. (Plate XIII. fig. 12.) 



Marma, triplo longior quam latior ; latere carinali per constrictionem angularem 

 bilobato ; carina granulis distinctioribus medio signata ; apicibus cuneato-obtusis ; valvis 

 vermiculatim striolatis. Ad Zebu. 



This superb Diatom was collected in the channel of Zebu among the Philippine Islands. 

 Its frustule, which is three times as long as broad, is angularly constricted in the middle, 

 and presents a bilobed aspect, the lobes forming wide curves. It is also marked by a row 

 of large granules, and the extremities of the valve are cuneately obtuse. The general 

 valvular ornamentation occurs in the form of tortuous lines of granules which intersect 

 each other. 



Nitzschia mammalis, n. sp. (Plate XXIX. fig. 5.) 



Mediocris, oblonga, sinuato-constricta ; apicibis productis, mammiformibus, carina 

 excentrica ; striis transversis. In mari Arafura. 



This frustule, which was obtained in the Arafura Sea, has an elegant oblong form and 

 a deep central contraction. Its transverse striation is uninterrupted longitudinally, and its 

 extremities are slightly prolonged and mammiform. 



Bacillaria, Gmel. 1 



"When the movements of Diatoms are considered, the peculiarities presented by those of 

 the genus Bacillaria are the most remarkable and mysterious of any. The genus includes 

 forms which are generally united to one another laterally, and in great numbers, and in 

 the living condition the individual frustules are constantly gliding over one another without 

 ever becoming completely disunited. Although various hypotheses have from time to 

 time been advanced to explain such wonderful phenomena, no observer has been able by 

 the most ingenious methods, by the use of the most perfect object-glasses or the most 

 efficient methods of illumination, to discover any special organs that might bring about 

 such curious results. 



When, by treatment with acids or by mechanical action, the frustules of the Bacillarice 

 become isolated from one another, their form may at first sight cause them to be con- 

 founded with species of Syncdra, Diatoma, or Nitzschia. Yet in the case of surface 

 gatherings it is easy, by placing the organisms in a glass cell before isolating the frustules 

 by the action of heat, to distinguish them by the characteristic disposition of the frustules 

 already referred to. 



By this means Bacillarian forms were frequently recognised in surface gatherings made 

 in the Sea of Arafura. The frustules were sublinear, lanceolate, and very slightly sigmoid. 



1 This genus was established by Gmelin in 1788 when he founded the species Bacillaria paradoxa (Linnaeus, 

 Syst. Nat., ed. xiii. vol. vi., 1788; Hassall, Freshwater Algoe, pi. xciii. fig. 10; Kiitzing, BacilL pi. xxi. fig. 

 18; Smith, Synop. Brit. Diat. vol. ii. p. 10, pi. xxxii. fig. 279, suppl. pi. lx. fig. 279. 



