Prof. W. Smith on the Diatomaceae of the Pyrenees. 3 



of the mouth of the Garonne, and known as the Bassin d'Arca- 

 chon ; here I had anticipated an abundant harvest of marine 

 forms, and my expectation would no doubt have been reahzed 

 but for the extreme heat of the weather, which suddenly assumed 

 a tropical character, drying up the smaller pools, and absolutely 

 forbidding active exertion. 



A few gatherings however furnished me with some interesting 

 species; among others, with Campylodiscus cribrosus and Nitzschia 

 scalaris, the latter having been long confined in its known 

 European distribution to the single locality in Poole Bay, where 

 I had first detected it as a British denizen, and only within the 

 last few months shown to have a wider range by its discovery 

 by Mr. Okeden in Milford Haven. This species is in several 

 respects important in reference to our present inquiry. Its 

 great size and conspicuous markings render it easy of detection 

 and identification, and the species-manufacturer has no excuse 

 for elevating its varieties into new forms, and thus destroying 

 its value as an index of geographical distribution. 



Ehrenberg's figure, as copied in Kiitz. Bacill. xxviii. 32, ia 

 quite characteristic, and he gives Surinam as its locality. His 

 only other locality of the recent frustule is Kourdistan, but this 

 freshwater station is open to suspicion. 



The references in the ^ Microgeologie ' to the presence of this 

 form in deposits are all worthless, as no description is given, and 

 the carelessness evident in the execution of the figures forbids us 

 to accept them as representations of our present species. The 

 ascertained distribution of Nitzschia scalaris is, therefore, from 

 the northern shores of South America to the southern coasts of 

 Britain, an area sufficiently large to establish the indifference of 

 this Diatom to the climatal influences of latitude. 



On the 3rd of July T proceeded to Biarritz. This is almost 

 the only point on the long line of shore extending from Brittany 

 to the Spanish frontier, where the coast is not low and sandy, 

 and in the holes and pools perforated by the turbulent waters 

 of the Bay of Biscay in the soft nummulitic rock, which here 

 attracts the admiration of the geologist, I made a few collections 

 that supplied me with two or three forms unknown to the British 

 flora ; these I have described in the sequel of this paper. 



On the face of the cliff beneath the Villa Eugenie, the new 

 chateau of the Empress of the French, I also made a freshwater 

 gathering, containing a new Epithemia, which, in compliment to 

 the locality and its amiable mistress, I have named Epithemia 

 Eugenice, 



On the 6th of July I proceeded through Pau to Eaux Bonnes 

 and Eaux Chaudes, and near the latter place, on the route to the 



I* 



