300 CAllPENTEK, ON rORAMINIFERA. 



of principal family types ; and any subordinate groupings of genera and 

 species which may be adopted for the convenience of description and 

 nomenclature, must be regarded merely as ass^eniblages of forms charac- 

 terised by the nature and degree of the modifications of the original type, 

 which they may have respectively acquired in the course of genetic 

 descent from a common ancestry. 



"4. Even in regard to these family- types, it may fairly be questioned 

 whether analogical evidence does not rather favour the idea of their deri- 

 vation from a common original, than that of their primitive distinctness. 



"5. The evidence in, regard to the genetic continuity between the 

 Fornminifera of successive geological periods, and between those of the 

 later of these periods and the existing inhabitants of our seas, is as com- 

 plete as the nature of the case admits. 



"6. There is no evidence of any fundamental modification or advance 

 in the foraminiferous type from the Palteozoic period to the present time. 

 The most marked transition appears to have taken place between the 

 Cretaceous period, whose foraminiferous fauna seems to have been 

 chiefly composed of the smaller and simpler types, and the commence- 

 ment of the Tertiary series, of which one of the earliest members was the 

 Nummulitic Limestone, which forms a stratum of enormous thickness 

 that ranges over wide areas in Europe, Asia, and America, and is 

 cliiefly composed of the largest and most specialised forms of the entire 

 group. But these were not unrepresented in previous epochs ; and their 

 extraordinary development may have been simply due to the prevalence 

 of conditions that specially favoured it. The Foraminiferous fauna of 

 our own seas probably represents a greater range of variety than existed 

 at any preceding period ; but there is no indication of any tendency to 

 elevation towards a higher type. 



" The general principles thus educed from the study of the Forami- 

 nifera should be followed in the investigation of the systematic affinities 

 of each of those great types of Animal and \'egetable form, which is 

 marked out by its physiological distinctness from the rest. In every one 

 of these there is ample evidence of variability ; and the limits of that vari- 

 ability have to be determined by a far more extended comparison than 

 has been usually thought necessary, before the real relations of their 

 different forms can be approximately determined. 



"As it is the aim of the physical philosopher to determine 'what are 

 the fewest and simplest assumptions, which being granted, the whole ex- 

 isting order of nature would result,' so the aim of the philosophic natu- 

 ralist should be to determine how small a number of primitive types may 

 be reasonably supposed to have given origin by the ordinary course of 

 ' descent with modification' to the vast multitude of diversified forms 

 that have peopled the globe during the long succession of geological ages, 

 and constitute its present Fauna and Flora." 



Dr. Carpenter divides the Foraminifera into two great 

 groups or sub-orders, the Imperforata and the Perforata. 

 The imperforate Foraminifera include the families Groraida, 

 Miliolida, and Lituolida. The perforate forms include the 

 Lagenida, the Globigerinida, and the Numulinida. These 

 families are divided into genera, and each generic form, recent 

 and fossil, with its recognised specific types and varieties, are 

 treated in great detail in the remaining chapters of the work. 

 It is impossible to give too much praise to this part of the 



