GASTROCOPTA. 



copta, but differing 1 by the development of other special fea- 

 tures of shape, umbilical region, or the like. They are un- 

 doubtedly local or regional derivatives of the old parent genus 

 Gastrocopta. In eastern Asia we have Boysidia and Hypse- 

 lostoma; in America, Chccnaxis, Bothriopupa, and perhaps 

 Gibbulina, all branches of the Gastrocopta trunk. As more 

 remote relatives, collateral genera which probably descended 

 from the same Mesozoic stock as Gastrocopta, we may men- 

 tion Fanxidus, Odontocyclas and Ab-ida (Torquilla). 



PAL/EONTOLOGIC HISTORY. As fossils, the Gastrocopts are 

 known only in the tertiaries of Europe. In the middle Oli- 

 gocene of Germany representatives of two subgenera, Albi- 

 nula and Sinalbinula, appear, presumably from an Asiatic or 

 Asiatico-American center of dispersal. Both continue in 

 abundance throughout the Upper Oligocene, Miocene and 

 Pliocene, in numerous specific mutations, but without much 

 structural progress. The fossils known throw no light on the 

 origin of the genus, since at least two of its minor divisions 

 had already been characteristically evolved prior to the 

 earliest appearance now known. The origin of the genus 

 must have been far earlier, Eocene or possibly Cretaceous. 

 Further notes, with illustrations, may be found in the section 

 treating of European species. 



DISPERSAL,. - - The migrations of so old a group as Gastro- 

 copta cannot be traced with any degree of certainty until its 

 paleontologic history is better known. It appears likely that 

 the main evolution of the group was in Holarctica, and espec- 

 ially in eastern Asia and North America, whence early emi- 

 grants penetrated into Europe and Australia, and later ones 

 into tropical America. In Australia the species remain rather 

 primitive in structure of the parietal and columellar lamellae, 

 the angular lamella being scarcely or but weakly united with 

 the parietal, even in the specialized group Australbinula. 

 None have the wholly concrescent lamellae of the progressive 

 Pliocene and recent Holarctic forms. This looks like an early 

 Tertiary radiation to that area. In South America the 

 Pupillidse (Gastrocopta, Immersidens, Pupoides) are closely 

 related to those of the Antilles and southern North America, 



