258 Dr. Greville o?? some British Diatomacese. 



the two frustules are viewed in connexion, the lines form a 

 symmetrical elliptical figure truncated at each end, for they are 

 very far from converging to a point. The median line of the 

 " internal cell," represented by Professor Smith's artist, is in 

 fact the junction of two frustules, A somewhat similar arrange- 

 ment appears to exist in Meridian Zincheni, Kiitz.*, as far as I 

 can judge from the figures given by the author, for I have not 

 had an opportunity of examining specimens myself. 



Among the interesting acquisitions made during the ex- 

 cursion, the first place must unquestionably be given to a very 

 minute form discovered in both Glen Callater and Canlochlan, 

 but extremely rare. Judging from the general character of the 

 frustules, Professor Smith was inclined to think that they be- 

 longed to a filamentous species, but being unfortunately all in a 

 scattered state, he could not with any certainty assign its place 

 in the system. He therefore, with some doubt, bestowed upon it 

 the provisional name of Grnmmatophora ? Balfuuriana. Having 

 had occasion to examine this most remarkable diatom minutely 

 in the preparation of this report, I have come to the conclusion 

 that Professor Smith is correct in referring it to one of the fila- 

 mentous groups. My reasons for coinciding in this view are — 

 1. That, apart from the peculiar structure, which of itself is 

 almost sufficient evidence, there is a greater variation in the 

 relative length and breadth of the frustules than would be likely 

 to occur in other diatomaceous groups. In some the length is 

 more than equal to twice the breadth, while others are exactly 

 square, and between these two extremes every gradation may be 

 observed ; resembling in this inequality, FragiUiria, Odontidium, 

 Grammatojjhora, and other filamentous genera having piano- 

 compressed frustules. 2. Two nodules exist at each extremity 

 of the frustule, as in Odontidium, Frayilaria, &c. 



AVith reference to the genus of this diatom I have ventured 

 to take a more decided course, as it does not appear to me that 

 it can be regarded even doubtfully as a Grommatophura without 

 doing violence to that genus. The vittse in the frustules of 

 Grammatophora are, to borrow a portion of Kiitzing's defi- 

 nition, " medio interruptse, plus minusve curvata? ;" they are, in 

 fact, with the exce])tion of this interniption, continuous through- 

 out ; whereas in the form under consideration they are as much 

 interrupted at each end as they are in the middle, and are be- 



* Professor Gregory informs me that this diatom was pointed out to him 

 bv De Brebisson in a gathering made by me last summer at DiuUlingston 

 Loch. I had not observed it ui , self, and Dr. Gregory's slide containing it 

 is not at the present moment accessible. Dr. Gregory has since observed 

 it in some Banffshire gatherings. 



