Recent and Fossil Foraminifera. 411 



talina, and figured and described incorrectly as Dcntalina nodosa* 

 d'Orbigny and Dcntalina subnodosa] Iteuss. When I found more 

 numerous examples of this species in the Westphalian Chalk 

 formation, and still later a second type, Pleurostomclla fusiformis, 

 and convinced myself of the constant irregularity of the chambers, 

 I was led to the closer inspection of the same, whereby I then at 

 once perceived the great variation in the form and position of the 

 opening, from which naturally and necessarily proceeds the above- 

 mentioned arrangement of the chambers. It was now impossible 

 to include these forms any longer with Dcntalina. 



" Apart from the great similarity to Dcntalina in the external 

 form, the chief difference lies in the aperture. Instead of the 

 same being round as in Dcntalina and situated on the end of the 

 last chamber, it represents a half-moon or even semi-elliptic 

 fissure, situated below the top of the chamber, on one side of the 

 same, and on the upper end of a larger or smaller depression 

 which has a raised edge. In consequence of this removal of the 

 position of the aperture from the highest point of the chamber, 

 the chambers no longer stand straight on one another, but each is 

 more or less inclined towards the side aperture of the preceding 

 chamber, so that the sutures take a slanting direction and the shell 

 a slightly undulating curve. 



" Moreover, the axis of the PleurostomelLne is either nearly 

 straight as in Nodosaria or slightly curved as in Dcntalina. The 

 shell substance is compact, shining like glass. 



" The two species of the genus at present known belong to the 

 Cretaceous formation, one to the white Chalk — the zones of Bclcm- 

 nitclla mucronata and B. quadrata — and the other to the Gault. 



" Pleurostomella subnodosa. — Length • 892 mm. Breadth 0*219 

 mm. Shell straight, rather thick, tapering only a little from below 

 to the blunt point, somewhat irregular (lit. knotted) owing to the 

 alternate slant of all the chambers. All sutures somewhat oblique, 

 especially those of the oldest chambers, and somewhat deep. The 

 chambers arched, especially on the side opposite to the bend. 

 The aperture lies on the upper end of a small, broad, oval, plate- 

 shaped depression, which only takes up a third part of the side 

 surface of the last chamber. It is crescent-shaped, and bounded 

 above and sideways by a sharp rim. Scarce." 



We here reproduce Eeuss' figures of Pleurostomclla subnodosa. 

 (PI. XI. fig. 3.) 



The genus Mlipsoidina was founded by Seguenza,f in 1859, 



* Reuss, 1845-46, Verstein. Bohm. Kreide, vol. i. p. 28, pi. xiii. fig. 22. (The 

 figure is very small and quite unrecognisable.) 



t Reuss, 1851, Foram. des Kreidemergels von Lernberg in Haidinger's Naturw. 

 Abhandl., vol. iv. p. 24, pi. i. fig. 9. (The small figure represents a straight right- 

 charnbered tapering Nodosaria.) 



% Seguenza, 1859. Eco Peloritano, Giornalo di Scienzc, Lettore cd Arti, 

 Anno V. serie 2, fasc. 9. Translated and edited by Brady in Ann. Mag. Nat. 

 Hist. 1868, ser. 4, vol. i. 



