OF BRITISH FRESH- WATER DIATOMACEiE. 9 



apparently by a line parallel to the outer margin, and this 

 border is very broad for so small a form. Length from '001 

 to -0012. Striae about 40 in -001 inch. 



30. Pinnularia subca/ntata, W. G. — This is another small 

 and linear species, which is found in the same gatherings as 

 the last, and also P. vaciva. It is linear, narrow, constricted, 

 subcapitate, the ends rounded. Tlie striae are subdistant, con- 

 spicuous, short. Length about "001 3". 



31. IHnnuIaria gracillima, W. G. — This species occurs in 

 the Elgin and Ekhies gatherings, in others from Banffshire, 

 and in various other localities. It is, I believe, the same 

 as that which Mr. Smith has named P. vaciva ; but 1 had 

 named it long before, and as Dr. Greville has adopted my 

 name in a recent paper in the Annals, I retain it. It is very 

 narrow and long in proportion, varying a good deal in length, 

 as from '0014 to "0025. It has a constriction towards the 

 apices, which again expand into longish rounded heads. 

 Striae fine but distinct ; I have not counted them. Dr. Greville 

 has found this species in the district of the Tummel and 

 elsewhere. 



32. Pinnularia digito-radiata, W. G, — This species occurs 

 in several gatherings from Duddingston Loch, also in Loch- 

 leven and elsewhere, and is not very rare. It is rather small, 

 in form linear elliptic or elliptic-lanceolate, and somewhat 

 narrow. It has a delicate aspect, and the striae are dis- 

 tinct, though rather fine, except at the centre, and much 

 inclined. The central nodule expands a good deal laterally, 

 and from it on each side diverge five or six very strong striae 

 or costae in a digitate fashion, as may be seen perhaps a little 

 too strongly marked in fig. 32. This character comes out 

 well under a high power. Length from •0014 to "002 inch. 

 Striae about -25 in 'OOl". This species has some resemblance 

 to the more finely striated varieties of what I have named 

 N. varians. But as N. varians occurs along with the new 

 form they are easily compared, and it is seen that the striation 

 of N. varians is much coarser and far more conspicuous, so 

 that the aspect of the two forms is quite different. 



33. Pinnularia Elginensis, W. G. — This species is another 

 of the numerous capitate forms which occur in fresh water. 

 It is rather small, not very narrow, with straight sides, con- 

 tracted towards the extremities, and again expanding into 

 somewhat square truncate heads. The nodule is rather inde- 

 finite, the striae not conspicuous but easily resolvable, fine and 

 very slightly radiate or inclined. It may possibly be a Navi- 

 cula, but it is often very difficult to know to which of these 

 two allied genera, Navicula or Pinnularia, we ought to refer a 



