Sketch of the Infusoria of the family Badllaria. 331 



group, appears necessary. Should the true age of either the 

 American or African deposits be determined by means of the fos- 

 sil infusoria, it will be an additional instance of the importance 

 of this branch of microscopic paleontology. It has been well 

 remarked that the microscrope is now as important an instrument 

 for the geologist as the hammer ; and indeed the results obtained 

 by microscopic observation of coal, fossil wood, teeth, polythala- 

 mia, and infusoria, prove the truth of this remark. The question 

 cui bono 1 to what useful end are your pursuits ? can now be tri- 

 umphantly answered by the lover of microscopic research ; but 

 happily, to use the words of the Hon. W. H. Harvey,* the class 

 who now ask this question to naturalists "is neither so numerous 

 or respectable as it was thirty years ago ; it is becoming every 

 day less so, and will soon be confined to the ignorant and the 

 sensual" In the language of another distinguished philosopher,! 

 " the time is past when the utility or dignity of such pursuits can 

 be affected by a sneer at the littleness of their objects, as they 

 seem little in the eyes of the indifferent and the ignorant. Every 

 thing is great or small only by comparison ; the telescope teaches 

 us that the world is but an atom, and none know better than mi- 

 croscopical observers that every atom is a world." 



Note. — Portions of the above paper were read before the As- 

 sociation of American Geologists at their meeting in Philadelphia 

 in April, 1841. 



Explanation of Plate 3. — The figures of this plate were drawn by 

 means of the camera lucida, and to the same scale as was used in 

 Plates I and II. 



Fig. 1. Synedra . One group of frustules, with part of an- 

 other, parasitic on aquatic plants in the Hudson River, a, fleshy base ; 

 h, fleshy projection at the summit. Brackish water. 



Fig. 2. Synedra , a, h, different positions. Fresh water, also 



fossil. 



Fig. 3. Podosphenia ? possibly a Gomphonema. Fresh water. 



Fig. 4. Gomphonema minutissimum, a, largest size ; b, smaller indi- 

 viduals. Hudson River near West Point. 



Fig. 5. Gomphonema , a, Z», different positions ; 5 c, sketch of a 



group of individuals with the branching pedicels. 



Fig. 6. Gomphonema acuminatum, a, i, different positions. Fresh 

 water, also fossil. 



* Manual of British Algae, by the Hon. William Henry Harvey. 



t Richard Owen, Esq. Address before the Microscopic Society of London, 1841. 



