DIATOMACEOUS DEPOSIT FROM, NORTH TOLSTA, LEWIS. 435 



30. Epithemia proboscidea, Kiitz. 



Common. Average length, 0-0350 mm.; greatest breadth, 0*0225 mm.; 

 breadth of valves (zonal aspect), 0*0075 mm.; and of connecting zone, 0*0085 mm. 



31. Epithemia rupestris, W. Sm. 



Less common than the preceding. The specimens agree in general form 

 with Smith's type, but the transverse costee are very distinct both in size and 

 appearance, being very much narrower and perfectly straight, instead of broad 

 and arcuate. 



Length, 0500 mm. ; greatest breadth, 0*0050 mm. ; average distance 

 between costae, 0*0025 mm. to 0*0030 mm. 



32. Eunotia tetraodon, Ehrenb. 



Very abundant, and typical ; ornamentation perfectly preserved. Length 

 (valval aspect), 0*0475 mm. ; greatest breadth, 0*0200 mm. ; height of median 

 dorsal ridges above median sulcus, 0*0050 mm. ; striae on middle of valve, 

 8 to 10 in 0*01 mm. 



33. Eunotia diodon, Ehrenb. 



Several frustules occur, but this species is by no means so abundant as the 

 preceding one. Length (valval aspect), 0*0500 mm. ; greatest breadth, from 

 concave side to apex of one of the opposite dorsal inflations, 0*0125 mm.; 

 breadth between dorsal ridges, 0*0100 mm. ; distance between apices of ridges, 

 0*0125 mm. (i.e.= breadth of valve across one of the ridges) ; striae in middle of 

 valve 10 in 0*01 mm. 



Although it is common for this species to have the transverse diameter at 

 the inflations considerably greater than that of the extremities, forms occur in 

 the deposit in which these diameters are nearly equal. The following are the 

 dimensions of one such specimen examined : — Length, 0*0825 mm. ; breadth of 

 terminal areas, 00100 mm. ; breadth at dorsal valval inflations, 0*0095 mm. 



34. Eunotia major (W. Sm.), Raben. 

 = Himantidium majus, W. Sm. 

 = Eunotia biceps and monodon, Ehrenb. 



Not unfrequent. The specimens exactly correspond to that figured by 

 Van Heurck (op. cit., pi. xxxiv. fig. 14), as far as the arrangement of striae in 

 slightly radiating lines is concerned, but the general outline of some of the 



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