Dr. Greville on some British Diatomacese. 255 



the additional tooth or undulation. Cayenne is the only locality 

 recorded by Kiitzing, but, like the preceding, it has probably 

 escaped notice on account of its minuteness. Since I detected 

 it along with E. tridentula in one of the Braemar gatherings, 

 Professor Gregory has observed it in those from Carr Bridge and 

 Ben Nevis. Dr. Walker-Arnott has also met with it, and it is 

 in Professor Smith's Hst from Auvergne. In this form, as well 

 as in E. tridentula^ the base is slightly concave, and there is a 

 small undulation near each end. 



Eunotia incisa, Greg. Length -0008". 



First observed and well figured by Professor Gregory in his 

 account of the rich fossil diatomaceous earth of Mull, published 

 in the ' Journal of Microscopical Science.' He has since found 

 it in various recent gatherings ; in fact, it appears to be very 

 generally diffused throughout the alpine districts of this country. 

 It is of frequent occurrence in the Braemar gatherings. I have 

 likewise seen it in fossil deposits from the United States. Pro- 

 fessor Smith, I believe, entertains some doubts whether this 

 diatom be a genuine Eunotia ; and it must be confessed that it 

 has much the aspect of a Himantidium, bearing a close resem- 

 blance in form to H. Veneris, Kiitz., as Professor Gregory has 

 remarked. Kiitzing however admits it as a new species, and as 

 the striation is that of a Eunotia, I feel disposed to retain it as 

 such. Although not strictly speaking a novelty, I refer to it in 

 this place chiefly in order to correct a slightly erroneous view 

 regarding the outline. In examining the frustule under a power 

 of three or four hundred diameters, there does appear to be an 

 incision or notch near each extremity of the frustule ; hence the 

 specific name. But on the application of higher powers the ap- 

 parent notch is found to be a deception caused by the nodule and 

 a slight contraction, commencing at the nodule and continued 

 to the apex. It is, in fact, the nodule interrupting the marginal 

 continuity of the frustule, which causes the appearance of an 

 incision. I find among living specimens quite as extensive a 

 range of form as is represented by Professor Gregory in the 

 paper above referred to. 



Cymhella cequalis, W. Sm. PI. IX. fig. 4. Length -0014''. 



A very distinct new species, so nearly symmetrical as to be 

 liable at a hasty glance to be taken for a Navicula. There is 

 however a curve at the shortly produced, obtuse extremities. 

 The striae are fine, but not very close. This form was abundant 

 in one gathering only, composed of coarse black peaty mud 

 extremely difficult to clean. 



