184 upper cretaceous-lower tertiary foraminifera 



Dimensions of described specimen. 



Maximum diameter = 0-33 mm. 



Minimum diameter = 0-25 mm. 



Thickness = 0-27 mm. 



Remarks. The holotype of G. velascoensis was described as being much compres- 

 sed with the sides very nearly parallel, in contrast to the strongly inflated, biconvex 

 forms here described, but Bolli (1957& : 71) stated that Cushman's holotype is a 

 poorly preserved and somewhat deformed specimen. Consequently, it would have 

 been quite justifiable to ignore Cushman's deformed holotype, and give the strongly 

 inflated forms described here a new name. However, as Cushman's deformed holo- 

 type still shows clearly the main characteristics of G. velascoensis as described by 

 White (1928), Bolli (1957&), and as shown in the present study, Cushman's name 

 is here retained. 



Subbotina (1953) described as Acarinina triplex forms which include both Globi- 

 gerina velascoensis Cushman and G. stonei Weiss. 



Specimens of G. velascoensis from the Esna-Idfu region conform well with those of 

 White (1928) and of Bolli (19576), although the latter described his forms as having 

 a smooth surface and a slightly concave dorsal side. 



The species is distinguished by its medium sized, inflated test, its strongly appres- 

 sed last chamber, its angular, depressed spiral suture and its 3^-4 chambers in the 

 last whorl which increase rapidly in size. It is also characterized by the shape of its 

 later chambers which are roughly oblong, with straight inner margins and distinctly 

 curved outer ones. 



Globigerina velascoensis was considered by Bolli (19576) to have evolved from 

 G. triangularis White, a probable junior synonym of G. triloculinoides Plummer, 

 although no direct evidence was recorded. However, as G. haynesi n.sp. was clearly 

 observed to have a tendency towards the development of an angular, depressed 

 spiral suture, a tightly coiled test, almost straight inner margins of the chambers in 

 the last whorl and a finely papillose surface, it may represent the ancestral stock from 

 which G. velascoensis evolved. The stratigraphical ranges of the two species are in 

 favour of this proposition, and forms of G. haynesi with a flatter dorsal side are 

 considered to be transitional to G. velascoensis. On the other hand, G. velascoensis is 

 believed to have evolved into G. stonei Weiss by the development of the heavily 

 nodose or even spinose surface, the chambers which increase more rapidly in size, the 

 wider umbilicus and the less appressed last chamber. Transitional stages between 

 these two species were recorded and their stratigraphical distribution also strongly 

 substantiates this proposition. 



Hypotype. P.45589. 



Horizon and locality. Figured specimen, from sample No. 51, Gebel Owaina 

 section. 



Stratigraphical range. The species was first described by Cushman (1925) 

 from the Velasco formation of Mexico where its stratigraphical distribution was 

 wrongly stated as Upper Cretaceous. It was also recorded from the same formation 



