OP THE GENERA NAVICULA AND CYMBELLA. 413 



I may mention here that Herkimer is a small town on the River 

 Mohawk, a mountainous stream cutting its way through a spur 

 of the Adirondacks, just a place for Cymbellae to live in, it being 

 well known that Cymbellae as a rule much favour clear moun- 

 tainous streams in alpine regions. And in reality the Herkimer 

 slide is full of various Cymbellae. 



The Monmouth-Cherryfield slides contain fossil forms ; both 

 these places are small towns in the State of Maine, not far from 

 the Atlantic coast on the line from Portland to Bangor, at about 

 43° N. This is interesting, as it seems that a relationship can be 

 traced between the Herkimer Cymbellae and the fossil forms of 

 the Maine deposits. Indeed, according to Cleve, some of the 

 Herkimer species, as for instance Cymhella Stodderi, are also to 

 be found in the White Mountains in the State of New Hampshire, 

 nearly at the same latitude between the Adirondacks and the 

 State of Maine. Before entering into specific details I would 

 mention that the Cymbellae described all belong to the " narrow " 

 or " naviculoid" type, very slightly asymmetric, and with both 

 margins convex. Some belong to the Encyonema group, living 

 in gelatinous tubes and with terminal nodules distant from the 

 ends — the chief characteristic of this group. 



The generic characteristics of the genus Cymbella are too well 

 known to be repeated here. I would add only a few remarks : 



(1) As far as I am able to observe, the central nodule, being 

 eccentric, may lie either on the ventral or on the dorsal side. 



(2) The terminal fissures are comma-like, and are turned in the 

 same direction, opposed to the side on which lies the central 

 nodule. 



(3) The raphe towards the ends seems to be always a little 

 arcuate or oblique, but towards the central nodule appears as if 

 it were slightly thickened, or as if it were approaching the upper 

 surface of the valve from below. Under low powers the oblique 

 part is usually invisible, but the thickened part is always seen. 

 This view is very characteristic of Cymbellae, even in the smallest 

 and least asymmetrical individuals. It is sometimes observable 

 even in those Naviculae which are intermediate to Cymbellae. 



(4) Some of the forms which I am going to describe show on 

 the median striae a punctum or stigma, more or less distinct. This 

 stigma causes the median stria to appear as if it coalesced with 

 the central nodule. According to van Heurck, this peculiarity 



