Notice of Ehrenberg^s Memoir on Microscopic Life. 309 



3. The whole number of microscopic forms included in this review 

 amounts to six hundred and three, of which four hundred and fifty are 

 Polygastrica, six Rotatoria, eight fragments of plants, (chiefly Phytoli- 

 tharia,) fifty six Polythalamia, and two other bodies. 



4. All of these six hundred and three minute American organisms 

 are included in one hundred and three genera, of which twenty five, 

 or almost one fourth, are new, but seventy nine, or about three fourths, 

 were already known and established. Of these one hundred and three 

 genera, sixty four (including six which are peculiar) belong to the four 

 hundred and fifty Polygastrica. . The six Rotatoria belong to five known 

 genera. The small forms, consisting of parts or fragments of organic 

 bodies, are assembled in eleven genera. The Polythalamia belong to 

 twenty genera, of which five are new and fifteen already known. 



Of the four hundred and fifty species of Polygastrica, two hundred 

 and fifty nine, or thirty four more than one half, were hitherto unknown, 

 and about one third are peculiar to America, but two thirds are Euro- 

 pean, Many of the forms here first named have recently been found 

 in Europe. 



In America as in Europe, the genera richest in forms are, Eunotia 

 with forty six species, Navicula and Pinnularia each with forty five 

 species. Then follow in the order of the number of species, the genera 

 Gomphonema twenty one, Cocconeis nineteen, Stauronei's eighteen, 

 Fragillaria, Surirella, seventeen. 



It is remarkable that all the genera distinguished as peculiar, have 

 presented but few and generally single species. 



5. Drawings of three hundred and twenty five American invisible 

 organisms are given, and three hundred and ten are first introduced 

 into the systematic list by short characteristics. 



6. These examinations have led to the establishment and systematic 

 review of two hitherto unconsidered great groups or families of mi- 

 croscopic bodies, which indeed are not independent organisms, but have 

 nevertheless the same worth for geological researches, viz. the uncrys- 

 talline siliceous bodies arranged under the family name Phytolitharia,* 

 and the organized calcareous fragments referred to the family Zooli- 

 tharia. Like all other species of fossils, these are suited to form a 

 good basis for geological conclusions. 



7. The eleven species whose names are given in the following list, 

 distinguish themselves from all others by their distribution, and con- 

 sequently their influence. They may be considered as cosmopolites, 

 ( Weltbiirger,) as they are found agreeing in character from the most 



* Various Phytolitharia are represented in this Journal, Vol. xliii, PI. 5, figs. 

 17 to 35, and in Hitchcock's Report on the Geology of Massachusetts, Vol. II, PI. 

 20, fig. 29. 



