76 THE VOYAGE OF H.M.S. [CHALLENGER. 



Memoir on the Marine Diatoms of Hong-Kong, annotated by Ealfs, and printed in the 

 Transactions of the Microscopical Society, new series, vol. iv. It runs thus : — " Frustules 

 smooth or minutely punctated, united with the adjacent ones by the interlacing of awns 

 proceeding from the frustule." I 



All the members of the genus CJi&toceros are extremely fragile, so that it is very diffi- 

 cult to distinguish them in deposits, especially in marine mud, in which only the more 

 robust forms are to be recognised, such as sporangial Goniothecia, Dicladise, or Syndendria. 

 On the other hand, filaments of Chsetoceros are much more abundant in surface collections, 

 being perhaps even the predominant forms, and among those collected in the Challenger 

 tow-nets, specimens belonging to the greater number of known species have been 

 observed. 



Chsetoceros" protuberans, Lauder, var. nov. (Plate VIII. fig. 2.) 



That a form of the Cli&toccros protuberans of Lauder;; is here represented is indicated 

 by the mammillar swelling on each valve, the outline of this protuberance being clearly 

 seen in the oval space intervening between two adjacent frustules. This species is described 

 by its founder as possessing minute bristly awns, but these are not to be observed in 

 the present frustule, and on consulting the plate of the typical form given by Lauder 

 minute bristles are only seen in connection with the terminal valves. If this is the 

 normal condition the specific definition given must be regarded as imperfect. Since, how- 

 ever, the series of frustules represented in our plate may be incomplete, the precise differ- 

 ences between the two organisms cannot be definitely fixed, although the varietal 

 character of the series at present in question may be provisionally accepted. 



Chaetoceros dispar, n. sp. (Plate VIII. fig. 6.) 



Frustula compressa, in seriern per longas setas teretes connexa a valvis procedentes, et 

 ad orio-inem constrictas : valvis alterne concavis et subconcavis. In mari Antarctico. 



This form shows several analogies to the Chsetoceros decipiens of Cleve, 3 but no traces 

 of striation or of punctation are to be found in the filaments or awns as in the allied type. 

 Moreover, the awns arise, not from the angle of the frustule, but exclusively from the 

 plane of the valve. At a short distance from their origin each filament presents a slight 

 swelling, and one of the valves is always more concave than the other, a circumstance 

 which has suggested the specific name. 



This species was found in the Antarctic Ocean. 



1 This latter definition, which does not exclude punctated forms, again illustrates the necessity that frequently 

 arises and that has already been referred to, for extending original definitions. 



2 Remarks on the Marine Diatomaceoe found at Hong-Kong, with descriptions of new species, Trans. Micr. 

 Soc. Lond., new series, vol. xii. p. 79, pi. viii. fig. 11, 1864. 



3 Diatoms from the Arctic Sea, Bihang k. SvensJca] Vet. Alcad, Handl., Band 1, No. 13, p. 11, pi. i. 

 figs. 5 a and 5 b. 



