297 



(ahnormal)? in Lewis's "Extreme and exceptional Variation of Dia- 

 toms in some "White Mountain Localities, etc," p. 11, PL II, 

 fig. 3 ; only the form figured by Lewis is somewhat more contracted. 

 It comes from '■'■Lafayette Mt. Lake''' (where it was found, together 

 with Tahellaria and Odontidium Tahellaria — now Fragilaria con- 

 struens). Lewis (1. c.) says: "This anomalous form suggests a 

 metamorphic variation — mediate between Tahellaria and Tetracyclus 



— and it is a true comprehensive type The relations of the 



septa, small as they are, to the valve and to each other, are con- 

 stantly those of Tetracyclus (never of Tahellaria), though the im- 

 pressible character of outline, passively yielding to the disturbing 

 force, has wandered far away from the typical pattern of that 

 genus." And he adds in a footnote : "The metamorphic force seems 

 to run riot in this particular locality (Mt. Lafayette Lake), and 

 nearly all the species appear to participate in this tendency to 

 depart from their normal type." Lewis therefore appears to regard 

 this form as an abnormality, and to have been led to do so by 

 the faet that almost all the other forms in the same gathering 

 showed a tendency to ahnormal development. — With regard to the 

 form found by me, there are no reason to regard it as an abnor- 

 mality, nor is there anything ahnormal in the two samples in which 

 it was found. In the sample from Krog-So (Lake Krog) it occurs 

 abundantly with Tab. flocculosa. Therefore I regard it as a well-defined, 

 normal species, possibly related to Tahellaria. It is scarcely identical 

 with Tahellaria binalis Ehr. in V. H., Syn., PI. XLIV, fig. 23 (from 

 Lillhagssjon). 



