234) Botanical Society of Edinburgh. 



Pinnularia tenuis. Cymbella tumens. 



P. parva. Gomphonema Brebissonii ? 



Stauroneis rectangularis, G. Hebridense. 

 Navicula apiculata. Smith. 



Professor Gregory then directed attention to the remarkable va- 

 riations of a form which had been referred by Mr. Smith to his 

 Pinnularia divergens, but, as found in the Mull earth, had more than 

 double the number of striee which belong to that species. It occurs 

 in several very striking varieties, and the conjecture was thrown out, 

 that it is in reality not P. diveryens, but a distinct species, including 

 P. stauroneiformis, P. interrupta and P. mesolepta of Smith, as well 

 as what he took for P. diver gens in the Mull deposit. 



Some remarks were also made upon the value of the generic and 

 specific characters of the Diatomacese. It was shown that the genera 

 Cymbella and Cocconema, Eunotia and Himantidium, seem to be re- 

 spectively separated on insufficient grounds. In regard to specific 

 characters, it was pointed out that while certain species vary almost 

 ad infinitum, others exhibit a remarkable degree of permanence. Ex- 

 amples of the former are Eunotia triodon, E. bigibba, Himantidium 

 bidens, H. undulatum, Pinnidaria divergens ; of the latter, Eunotia 

 tetraodon, E. Diadema, Navicula Trochus, N. serians, N. rhomboides, 

 Pinnularia alpina. It was thought that these very characters of per- 

 manence and variableness might be usefully employed as specific cha- 

 racters, and that viewed in this light, each of them afford strong 

 proof of the real existence of species as natural divisions. 



Professor Gregory has still several new forms found in this deposit 

 to describe on some future occasion ; and he is engaged in the 

 study of other deposits, in all of which he has already found species 

 hitherto overlooked, and among these several of the new forms above 

 named. 



2. " On the occurrence of Desmarestia Dresnayi on the coast of 

 Ireland," by W. Sawers, Esq. 



In a letter to Professor Balfour, Mr. Sawers states, " I have great 

 pleasure in sending you specimens of an Alga new to the shores of 

 the United Kingdom. Specimens having been sent to Dr. Montague 

 of Paris, he writes, that he gathered the same plant at Fort St. Se- 

 bastian, Spain, in 1823, published a description of it, with a plate, in 

 1842, in the 'Annales des Sciences Naturelles,' naming it Desmarestia 

 pinnatinervia, and that it has been found by M. Crouan at Brest, 

 though rarely. M. Crouan makes it a variety of Desmarestia Dres- 

 nayi, but M. Montague maintains the distinctness of his species 

 and retains his name D. pinnatinervia. I found the young fronds 

 floating early in August at Moville, near the mouth of Loch Foyle, 

 and have visited the locality frequently since, always getting a num- 

 ber of specimens, the great majority imperfect. When fresh, it has 

 the colour of a Laminaria, but is not so glutinous to the feel, and 

 thinner. The root is a disc, and sometimes two or three fronds 

 arise from the same disc ; in some cases they are slightly proliferous 

 where the margin has been injured. The frond is from 12 to 18 



