STUDIES IN rORAMINIFERA 



1^9 



convex. Umbilicus very narrow. Periphery moderately 

 to strongly lobate and broadly rounded. Chambers 

 inflated, 9-13 in number, all visible spirally, only 

 4 to 4:% (very rarely 5) of last whorl visible on umbilical 

 side. Sutm"es distinct and depressed, straight and 

 radial except in initial whorl where they are curved 

 backward. Wall calcareous, thin, finely perforate, 

 practically always perfectly smooth. Aperture large, 

 an arch at base of final chamber, extending from um- 

 bilicus to a point near periphery, bordered by distinct 

 lip. Aperture of penultimate chamber occasionally 

 visible in umbilicus. Gerontic specimens develop 

 strongly inflated chambers in last whorl; final chamber 

 is displaced toward umbilical side, and occasionally 

 carries accessory aperture on spiral side. 



This species is characteristic of the Danian stage in 

 Denmark and Sweden and does not occur in the under- 

 lying Maestrichtian White Chalk. In the basal part 

 of the overlying S^landian beds, reworked (?) specimens 

 have been observed. 



The present form might be considered a chronological 

 subspecies, but it might also be a geographical sub- 

 species, produced by the hydrographic conditions in 

 the enclosed Danian sea (cfr. G. bulloides, which ac- 

 cording to Brady (1884, pi. 79, figs. 1-7) develops a 

 dwarfed and smooth (?) test near the British coast). 



Coiling ratio: Basal Danian: Bogelund, 49. per- 

 cent dextral (±4.9); north of Holtug quarry, Stevns 

 Klint, 48. percent dextral (±9.). Zone of Tylocidaris 

 odumi: Hojerup, Stevns Klint, 56.9 percent dextral 

 (±6.); Boesdal, Stevns Klint, 51. percent dextral 

 (±3.9). Zone of T. brunnichi: Fakse, 76.9 percent 

 dextral(±11.7). 



Dimensions: Specimens range in greatest diameter 

 of test as foUows: Basal Danian (Bogelund), 0.16-0.29 

 mm.; zone of Tylocidaris odumi (Stevis Klint), 0.29- 

 0.34 mm. (gerontic specimens, 0.40 mm); ? zone of T. 

 odumi (Hjerm), 0.26-0.34 mm.; Zone of T. abildgaardi 

 (Stevns Klint), 0.17-0.19 mm.; zone of T. briinnicM 

 (Fakse), 0.17-0.20 mm.; zone of T. vexilifera (Ostra 

 Torp), 0.16-0.24 mm. 



Globigerina triloculinoides Plummer 

 Plate 30, Figure 4 



Globigerina triloculinoides Pltjmmeb, Univ. Texas Bull. 2644, pp. 



134-135, pi. 8, fig. 10, 1926. 

 Non Globigerina triloculinoides Brotzen, Sveriges Geol. 



Undersokning, ser. C, No. 493, pp. 89-90, pi. 17, fig. 2, 1948. 



Remarks: The distinctive features of this highly 

 variable species are (1) the pitted (reticulate) sirrface, 



(2) the inflated, globular chambers, (3) the smaU and 

 shallow umbilicus, and (4) the small aperture, which is 

 covered by a distinct lip. 



The occurrence of the species in the Midway group of 

 North America has been mentioned above. 



The species reported by Brotzen (1948) from the 

 Danian stage of Sweden as O. triloculinoides has a some- 

 what trochoid spire and the volutions increase more 

 slowly in width than do those of the typical 0. trilocu- 

 linoides. Brotzen's specimens may perhaps be refer- 

 able to 6. daubjergensis Bronnimann. 



Coiling ratio: Zone of T. briinnicM: Fakse, 100 

 percent dextral (11 specimens counted). Zone of T. 

 vexilifera: Ostra Torp, south Sweden, sample 2 (see 

 text-fig. 24), 47.8 percent dextral (±7.); same locality, 

 exact level unknown, 81.8 percent de.xtral (±11.6). 

 Additional data are needed before the question of the 

 variation in coiling ratio of this species can be satis- 

 factorily answered. 



Dimensions: Specimens range in greatest diameter of 

 the test as follows: ? zone of Tylocidaris 6dumi (Hjerm), 

 0.20-0.27 nam.; zone of T. briinnicM (Fakse), 0.19-0.22 

 mm.; zone of T. vexilijera (Ostra Torp), 0.14-0.26 mm. 



Clobigerina compressa Pluininer 



Plate 30, Fiqubb 5 



Globigerina compressa Plummer, Univ. Texas Bull. 2644, pp. 

 135-136, pi. 8, fig. 11, 1926. 



Remarks: Bronnimann (1953) placed this species in 

 the genus Oloborotalia, but the present writer agrees with 

 Brotzen (1948, p. 90) that it should be referred to the 

 genus Olobigerina inasmuch as it possesses "a distinct 

 umbilicus and umbilical apertures, covered by small 

 lips on the base of the last chambers." This character 

 has also been observed in specimens from the Mexia clay 

 member of the Wills Point formation (upper Midway 

 group). There is good agreement in all respects be- 

 tween the specimens from the Danskekalk formation 

 and those from the Midway group. 



Coiling ratio: ? Zone of Tylocidaris odumi: Hjerm, 

 only 3 specimens available. Zone of T. vexilijera: 

 Ostra Torp, south Sweden, sample 1 (see text-fig. 24), 1 

 specimen; same locality, sample 2, 50 percent dextral 

 (±14.); same locality, exact level unknown, 63.6% 

 dextra (±14.5). 



Dimensions: Specimens range in greatest diameter of 

 the test as follows: ? zone of Tylocidaris odumi (Hjerm), 

 0.22-0.26 mm.; zone of T. vexilijera (Ostra Torp), 

 0.16-0.30 mm. 



