GEOLOGIC DISTRIBUTION 45 



is probably due to lack of earlier records rather than that these 

 represent the first records of the group. The Silicinidae appear 

 in the Lias, more of the Miliolidae and Ophthalmidiidae are 

 developed. The earliest unmistakable primitive genera of the 

 Buliminidae and Rotaliidae also appear, but not the more 

 specialized families derived from the Rotaliidae. 



There are very few large species of foraminifera in the 

 Jurassic, but the faunas have many smaller ones. For the first 

 time the calcareous types, as represented by the Lagenidae par- 

 ticularly, predominate over the arenaceous forms although in 

 some horizons the latter are abundant. 



With the Lower Cretaceous there is a great development of 

 new forms. Arenaceous forms continue as they do to the Recent 

 oceans, but they are largely overshadowed by the calcareous 

 forms. More of the genera of the Buliminidae appear such as 

 Virgulina and Bolivina. In the Rotaliidae a few more of the 

 primitive genera appear. The Globigerinidae make their first 

 appearance with undoubted species, and the Heterohelicidae 

 appear although better developed in the Upper Cretaceous. The 

 simpler forms of the Anomalinidae appear. Of the large forms, 

 Orhitoliyia becomes very abundant. 



The Upper Cretaceous greatly increases the number of genera 

 that are developed. Many of them such as Pseudotextularia, 

 Piano glohulina, Eouvigerina, etc., became extinct in America 

 with the Cretaceous although in Europe they apparantly per- 

 sisted into the Lower Eocene. With the Upper Cretaceous there 

 are new families appearing, especially the more specialized ones 

 derived from the Rotaliidae such as the Calcarinidae, 

 Chilostomellidae, Globorotaliidae, Peneroplidae, and theOrbitoid- 

 idae. Some of these may be found to have had their real 

 beginnings in the Lower Cretaceous. Pelagic foraminifera 

 appear to have been first definitely developed in the Cretaceous. 

 The Globigerinidae and Globorotaliidae were well developed and 

 abundant, and the Guembelinas seem to have been pelagic at this 

 time although none of their group are pelagic today. In general, 

 the Upper Cretaceous takes on many modern aspects in the 

 foraminifera although in many respects it is primitive. The 

 specialized groups of this period have mainly disappeared. 



With the Eocene, modern forms are more abundant. Large 

 species are developed in the warm seas of this time. The genera 



