REPORT ON THE PIATOMACE.E. 67 



prora, while the general characters of the shell prevent it from being confounded with the 

 Syned/rce. 1 



The NitzschicB are abundantly represented, both in freshwater and in marine col- 

 lections ; but in the latter case they especially belong to the littoral flora, a circum- 

 stance which sufficiently explains the fact that observers have in recent times failed 

 to meet with so many new species of this genus as in the case of many others which 

 do not flourish so abundantly in the neighbourhood of the sea-shore. Among the 

 numerous soundings made by the Challenger in different localities many species 

 of the genus were recognised, but of these only the following are worthy of special 

 attention : — 



Nitzschia plana, W. Sm., var. zebuana, nov. (Plate XIII. fig. 10.) 



This specimen greatly resembles the Nitzschia plana of Smith 2 when its outline is con- 

 sidered, although its extremities can hardly be called acute. Its valve is obscurely striated, 

 while the keel, instead of bearing a single band of larger granules, is marked at 

 intervals by small irregularly disposed but very prominent lines. It is also to be borne in 

 mind that the species of Smith is a brackish-water form, while the present frustule is 

 marine, having been collected in the canal of Zebu among the Philippine Islands. Not- 

 withstanding these differences the latter must be viewed as only a variety of the former, 

 especially when the great resemblance of the two forms and the identity of the interrupted 

 striation of the two valves is kept clearly in view. 



Nitzschia obesa, n. sp. (Plate XIII. fig. 11.) 



Duplo longior quam latior ; medio angulariter constricta ; apicibus obtusis ; striis 

 dense decussatis ; carina lata distinctioribus lineolis inordinate signata. In mari Philip- 

 pinarum prope Zebu. 



This form, which is also from Zebu, is remarkable in being only twice as long as it is 

 broad. It is angularly constricted in the middle, its extremities are obtuse, and the striae 

 are densely decussate. The valve is flanked by a large keel, which is traversed by prominent 

 lines of irregular distribution and direction. 



Nitzschia obesa, n. sp., var. nov. (Plate XIII. fig.. 13.) 



We have here represented a frustule from the port of Tahiti, which is somewhat less 

 obese than that just described, and which is provided with somewhat cuneate extremities. 

 Its striation, however, is of equal delicacy, and the keel though narrower bears short 

 but equally prominent lines. From such characteristics it can only be looked upon as 

 possessing a varietal importance. 



1 See Pritchard, op. cit., p. 779. 2 Synopsis of the British Diatomaceae, vol. i. p. 42, pi. xv. p. 114. 



