220 PROCEEDINGS OF THE ACADEMY OF [Mar., 



one per cent., of which magnesium and sodium salts constitute a 

 considerable portion." 



The following is the diagnosis of the form: 



Filaments straight, 23;^ wide. 



Cells rectangular with sharp angles; valves slightly convex; 

 foramina narrowly linear, irregular, bipartite. 



Setae straight, hollow, approaching each other at an acute angle 

 and crossing at a right angle near the corners of the valves, about 

 ten times the length of the valve. In valve view they diverge from 

 each other at an angle of about 80°. 



Terminal setaj shorter than the others, somewhat curved in the 

 direction of the filament. 



Spores with the primary valve arcuats, secondary valve produced 

 into a subconical frustum. Rarely in free spores the primary valve 

 is covered with minute spines. 



The valves are joined together near one side by a tubular com- 

 missure, from six-tenths to eight-tenths of a micron in thickness, 

 situated near the edge of the valve, usually at unequal distances 

 from each end, and, so far as noticed, is found near the margin on 

 the same side of all valves in the filament. 



The presence of the connecting tube and the unusual locality 

 combine to render this form a unique species, which I take pleasure 

 in naming after Prof. Elmore. 



An examination of fig. II, i and k, in Plate III, in Schiitt's article 

 {Ueber die Diatomeengattung Chwtoceros, Bot. Zeitung, 1888) offers 

 an interesting suggestion as to the origin of the commissure. In 

 the genus Thalassiosira the cells are connected by mucilaginous 

 threads which are central. In the present species of Chcetoceros the 

 commissure is eccentric and appears to be tubular. In C. simile the 

 valves touch each other, and in several species, such as cojnpactnm, 

 the centre of the valve is produced or considerably elevated, but 

 in no previously descril^ed form has the union of the frustules been 

 consummated, except by the interlacing of the awns. 



The other diatoms sparingly found in the waters of the lake include 

 species of Fragilaria, Gomphonema, Epithemia, and Surirella. Owing 

 to the presence of great quantities of small Crustacea, the material 

 is mounted with difficulty. 



Explanation of Plate X. 



Fig. 1. — A short filament consisting of sc'vcn cells. The filaments usually contain 

 twenty or more cells. In filaments showing the spores, the width is quite 

 constant, but in vegetative cells the width varies considerably, many of 

 them being much wider. 



