Sketch of the Infusoria of thefamily Bacillaria. 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 ? 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,t 
“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 rade at their meeting in Philadelphia 
in April, 1841. 
Explanation of Plate 3.—The fo of this plate were drawn. by 
means of the camera lucida, and to the same scale as was used in 
Plates I and IL : 
Fig. 1. Synedra . One group of frustules, with part of an- 
other, parasitic on aquatic plants in the Hudson River. a, fleshy es 
b, fleshy projection at the summit. Brackish water. 
Fig. 2. Synedra , a, b, different positions. Fresh water, also 
fossil. 
Fig. 3. Podosphenia? possibly a Kieenphbnite Fresh water. 
Fig. 4. Gomphonema minutissimum, 4, largest size; b, smaller indi- 
Viduals. Hudson River near West Point. 
Fig. 5. Gomphonema , a, b, different positions ; 5 ¢, sketch of a 
group of individuals with the branching pedicels. 
Fig. 6. Gomphonema acuminatum, 4, b, different positions. Fresh 
picid also fossil. 
* Manual of British Alge, by the Hon. bide om Henry berth i 
- + Richard Owen, Esq. am, eal 
