8 PROCEEDINGS OP THE ACADEMY OF 



tains Surirella intermedia, S. anceps, S. delicatissima, Eunotia incisa, c, along 

 with recent species. 



These localities are all within the range of glacial influence. 



After a careful examination of the slides, prepared from gatherings from 

 these localities, I have been struck not only by a general correspondence in 

 their species and varieties to those of the Saco and Wolfboro muds, but also 

 by their unlikeness to species and varieties outside the White Mountain tract. 

 In speaking of the Saco and Wolfboro species I alluded to their general re- 

 semblance to those of the sub-peat and peat deposits ; the same remark of 

 course holds good in reference to Mr. Stodder's localities. I will here simply 

 confine myself to the statement of this general resemblance which further on 

 will be illustrated by a table of species. 



There is one point, however, relating to the curious tendency to variation, 

 usually on a definite direction, apparent in many of these localities in com- 

 mon with post-tertiary deposits in other northern sections of this country, 

 which requires ft passing notice. 



This tendency, which for convenience I shall call metamorphic, seems to co- 

 incide with the abundant introduction of certain genera in new localities. It 

 is marked by a singular relaxation of the laws governing what I have before 

 termed the non-essential characters of genus ; in other words, while respecting 

 the more fixed and positive generic characters (essential,) as alee, canaliculi, 

 median lines, nodules, c, it would seem to exhaust its influence on the more 

 general and unimportant ones, as size, outline, striation, &c, common to all 

 diatoms (non-essential.) 



Besides the intermediate or comprehensive type already spoken of, there would 

 appear to result from this metamorphic tendency a subjective variation in many 

 co-existing genera whether allied or not to the incoming one. This variation, 

 which is not always special in its direction towards any type or genus, affects 

 principally the size, form, valvular outline and striation of many species, 

 manifesting itself oftenest in a disposition to assume an undulate, crenulate, 

 apiculate or even cruciform shape ; more rarely to lose these characters. It 

 would seem to originate in a superabundance of the sporangial element, and 

 frequently begets irregular, abnormal or unsymmetrical forms, according to 

 the more or less spasmodic or intermittent action of the disturbing force. I 

 may add that, in accordance with a well known law, most of these so formed 

 varieties, where involving alteration of generic characters, as Surirella interme- 

 dia, S. anceps, &c, or where irregular and unsymmetrical, as Actinella, either 

 rapidly disappear by a process of degeneration (visible in S. intermedia,) or 

 revert to the normal type, while the extreme varieties, not implicating generic 

 character, on the other hand may often become more or less permanent, as in 

 Navicula Jirma, N. rhomboides, N. serians, and others. 



To render more intelligible what I have tried to explain above, I shall now 

 notice a few of the most remarkable varieties contained in the Saco spring, 

 Wolfboro, and Mr. Stodder's localities. 



(1.) " Navicula sekians" (Kutz.) " V. acute ; transverse stria? faint, 60 in 

 100; longitudinal distinct, 36 in -100 :" frustules often cohering: Length 

 0017" "to -0035"," (Smith.) 



(2.) Var. a {apiculate.) V. varying from lanceolate elliptic to rhomboid, 

 with apices more or less produced and capitate (fig. 5a, pi. ii.) 



(3.) Var. b (cruciform.) N.follis, (Ehr.) =N. inflata, (Ehr.) ? "V. much 

 inflated, compressed, sloping abruptly towards the produced and often trun- 

 cate apices ; extreme variety cruciform," (fig. bb, pi. ii.) 



Var. a. (apiculate) about two-thirds, and Var. b. (cruciform) less than one- 

 half the length of the typical form. 



Striation in both varieties beyond a certain distortion on the latter variety 

 precisely resembling that of the typical form. 



[Jan. 



