STUDIES IN FORAMINIFERA 



227 



Type and occurrence: Holotype (BMNH P41659) 

 here figured, from the Lower Crag (PHocene) of Sutton, 

 Suffolk, England. 



? Family Virgulinidae Cushman, 1927 

 Aeolostreptis Loeblich and Tappan, new genus 



Plate 72, Figure 20 



Type species: Buliminella vitrea Cushman and 

 Parker, 1936. Derivation: aiolos, Gr., changeable + 

 streptos, Gr., twisted; gender feminine.) 



Test free, elongate, base bluntly rounded, the early 

 portion in a low discorbine coil with sLx chambers per 

 whorl, later reduced in number to three chambers per 

 whorl, and becoming high spired; chambers few in 

 number, at first low, later about equal in breadth and 

 height, but never extremely high and elongate; sutures 

 distinct, depressed; wall calcareous, finely perforate, 

 granular in structure, surface smooth; aperture a loop 

 at the inner margin of the final chamber, at right angles 

 to the sutures, with a narrow lip at the forward margin. 



Remarks: Aeolostreptis, new genus, differs from 

 Lacosteina Marie in the early coil being trochoid as in 

 Discorbis Lamarck, rather than planispiral, and in 

 there being a gradual increase in the height of the spii'e 

 instead of an abrupt change in the plane of coiling from 

 the early coil to the later spire. 



Buliminella Cushman differs in having a radial rather 

 than granular wall structure and a tapered rather than 

 bluntly rounded base, due to the type of chamber 

 arrangement. Buliminella has an increasing number of 

 chambers per whorl \vith later development, and has a 

 complex internal toothplate, whereas Aeolostreptis has a 

 decreasing number of chambers in later development. 



The majority of species with few chambers in the last 

 whorl, placed in Buliminella by Cushman and Parker 

 (1947), are in reality species referrable to Praebulimina 

 Hofker, since typical Buliminella apparently is not 

 foimd below the Eocene. Aeolostreptis, new genus, 

 diflfers from Praebulimina in having the early many- 

 chambered coil forming a bluntly rounded base, instead 

 of being triserial throughout and increasing gradually 

 in diameter. 



It resembles Virgulina m having a granular wall, un- 

 like the radial-walled Buliminidae, but has an early 

 spire, rather than a twisted biserial development. It is 

 therefore referred to the Virgulinidae questionably for 

 the present. 



Types and occurrence: Holotype of Buliminella 

 vitrea Cushman and Parker (Cushman Coll. 22575), 

 paratypes (Cushman Coll. 32550) from the Selma group, 

 Dermopolis chalk (Campanian), 2 miles west of Gun- 

 town, Mississippi. Collected by G. M. Ponton. 



Figured hypotype (Cushman CoU. 32549) from 

 chalk of the Selma group, 1 1 K miles east of Blue Springs, 

 Mississippi. Unfigured hypotjrpes (Cushman Coll. 

 32547) from chalk of the Selma group, 1 mile west of 

 Tupelo, Mississippi. Unfigured hypotypes (Cushman 

 Coll. 32548) from chalk of the Selma group, 1 mUe east 



of Booneville, Mississippi. All hypotypes collected by 

 G. M. Ponton. 



Family Virgulinidae Cuslmian, 1927 



Sigmavirgulina Loeblich and Tappan, new genus 



Plate 73, Figures 1, 2; Text-figure 30 



Type species: Bolivina tortuosa Brady, 1881. (Deri- 

 vation: sigma, Gr., letter S -f Virgulina, genus of 

 Foraminif era ; gender feminine.) 



Test free, biserial, with chambers added slightly 

 more than 180° apart, forming a sigmoiline type of 

 an-angement with two series of chambers at first 

 forming a tight low sphe, later developing a higher 

 spire, and appearing almost regularly biserial although 

 somewhat twisted throughout, periphery angled or 

 with a distmct keel, chambers numerous, increasing 

 regularly in height as added, increasing more rapidly 

 in breadth so that the test is flaring; sutures distinct, 

 thickened, depressed; wall calcareous, of calcite (by 

 X-ray determination), coarselj' perforate, granular in 

 structm-e, surface smooth or with short spines, espe- 

 cially in the early portion ; aperture at the inner margin 

 of the final chamber, an elongate oval, surrounded by 

 a lip which passes gradually into the peripheral keel, 

 in some specimens the aperture may tend to become 

 terminal, and is situated a short distance above the 

 base of the chamber. 



Remarks: Sigmavirgulina, new genus, differs from 

 Bolivina d'Orbigny in having a granular instead of a 

 radial wall structm-e, in the early sigmoiline type of 

 development, and the twisted adult test resulting from 

 this process. Typical Bolivina may also have fingerlike 

 extensions of the chambers extending back over the 

 preceding sutiu-es. 



Sigmavirgulina is thus much closer to Virgulina 

 d'Orbigny in having a granular waU and a twisted 

 biserial test. It differs in having a compressed rather 

 than rounded test, broad low chambers rather than 

 very high and elongate ones, and a coarsely perforate 

 test. 



Figure 30. — Outline camera lucida drawing of basal view of Sigma- 

 virgutina tortuosa (Brady) to show spiral biserial chamber arrange- 

 ment and sigmoid curve of plane of biseriality. P, proloculus, 1-7, 

 and l'-6' showing the two spiralling series of chambers. X 125. 



Numerous references in the past have erroneously 

 stated that Virgulina has a triserial base. Topotypes 

 of the type species, V. sguammosa d'Orbigny, from the 

 Pliocene of Italy, when examined from the base show 

 the same highly twisted biserial development as in 

 Sigmavirgulina. Those species with a true triserial 



