324 NEW MICROSCOPIC ALG^. 



Another form, which I am unable to identify with any previ- 

 ously described, is 



Navicula pseudo-libellus, n. sp. T. W. 



Valve very narrow, elliptic-lanceolate, slightly constricted 

 towards the extremities, which are slightly rounded and pro- 

 duced; front view very broad, pseudo- annulate; stri^ indistinct. 

 Length of valve, -001 ; breadth, -0003. (Plate XVI., fig. 9.) 



Remembering the almost innumerable hosts of Naviculce^ and 

 the difficulty of marshalling them, it is with the greatest reluc- 

 tance I describe the present as a " New Navicula." But it really 

 appears to differ sufficiently from all others hitherto described, in 

 the unusual development and longitudinal striation of the con- 

 necting membrane; the only other Naviculoid form I am ac- 

 quainted with resembling it in these respects being N. rhombica, 

 Greg., which is by many observers considered to be Schizonema 

 GrevilUi. I am haunted by the idea that Dr. Gregory also de- 

 scribed a somewhat similar but much larger form under the 

 name of N. libellus, but though hours have been spent in hunting 

 for it amongst his numerous contributions, I can nowhere light 

 upon it. 



The form now under notice has been found abundantly by ]\ir. 

 Atthey, nearly pure, at Cullercoats Bay, in July of the present 

 year : from its peculiar form it is difficult to obtain a sight of the 

 side view. 



Navicula cryptocephala. 



Another little Navicula, gathered plentifully on the sands 

 north of the Coquet, I am compelled to consider (for the pre- 

 sent at least) as N, cryptocephala, Mr. A. says, in a letter accom- 

 panying a slide of it — " Where it was collected the tide flows, 

 I should think, twenty yards farther out every tide, yet, when the 

 tide is at ebb, water oozes out over the sands." Should it eventu- 

 ally prove to be the form here supposed, the capability of the 

 existence of Navicula cnjptocephala in salt, brackish (when the tide 

 is out), and fresh water, will be an interesting addition to our 

 knowledge of habitats of the Diatomacece. 



