216 Messrs. Parker and Jones on 



with but little perspective, and rarely with both faces of the 

 shell, the student still finds himself too frequently at fault. 

 The perfect engraving of shell-structure, tubes, pores, opacity, 

 granulosity, &c., of septa, septal orifices in many cases, and 

 other details, gives the majority of the figures great value ; 

 and, besides the evident truthfulness of form and structure, 

 the picturing of accidental air-bubbles and contents of cham- 

 bers (coloured sometimes) shows how exact and conscientious 

 has been the artistic labour bestowed on the work. 



In reading aright the generic and specific relations of Dr. 

 Ehrenberg's Foraminifera, drawn so carefully in the splendid 

 plates of the ' Mikrogeologie,' we have to remember that they 

 are mounted in Canada balsam and seen by transmitted light; 

 and, indeed, it requires an experienced acquaintance, almost if 

 not quite as complete as that of Ehrenberg himself, with simi- 

 larly mounted Foraminifera, from all parts of the world, to be 

 enabled to detect and realize the zoological value of faint dif- 

 ferences of apparent convexity and of opacity, punctation, 

 porosity, and granulation, of relative thickness of shell-walls, 

 whicli sometimes look like marginal keels, — of imperfect in- 

 dications of the position, direction, and form of septal aper- 

 tures, rarely shown except, as it were, in section, — and of 

 other characteristic details which go to make the recognizable 

 fades of a species or variety. 



Few of the specimens figured are more than -gV of a Paris 

 line in diameter — that is, invisible to the naked eye. They are 

 such as are readily Avashed away during the process of disin- 

 tegrating soils, muds, and friable shales, marls, and chalk by 

 means of water ; whilst, on the contrary, such Foraminifera 

 as have been figured by other authors are mostly those that 

 remain after the muddy or chalky water has been poured ofi^ 

 in the preparation, and can be readily picked out with the aid 

 of a pocket-lens. 



We cannot choose a better opportunity than the present to 

 introduce the Cordial and truthful expression of an accom- 

 plished American naturalist's well considered opinion of the 

 great German microscopist's labours and expositions. Treat- 

 ing * of Ehrenberg's description of microscopic organisms 

 from America, he says : — 



" This important memoir by the illustrious Ehrenberg is 

 characterized, like all the preceding works of this author, not 



* Americ. Journ. Sc. Arts, vol. xlvi. April 1844: Notice of a memoir 

 by C. G. Ehrenberg, " On the Extent and Influence of JNIicroscopic Life 

 in North and South America," pp. 297-313. 



