1897.] 



of Triloculina and Biloculina. 



237 



In the microspheric form of this genus however, as has been 

 admirably shown by M. Schlumberger, the arrangement of the 

 chambers is at first on a different plan (Fig. 3), namely, that 



Fig. 3. Transverse section of the microspheric form of the same species, x 90 

 (Two external chambers have been omitted from the figure.) 



which characterises the genus Quinqueloculina during its whole 

 growth. In the shells of this genus (Fig. 4) the chambers are 



Fig. 4. Transverse section of the megalospheric form of Quinqueloculina 

 undulata d'Orb. x 100. 



Figs. 1 — 3 are from Schlumberger, " Kevision des Biloculines des grands fonds." 

 Mem. d. I. Soc. Zoologique de France, Tome iv. ann6e 1891, p. 155. Figs. 1, 2, and 4. 

 Fig. 4 from " Monographie des Miliolid6es du Golfe de Marseille," by the same 

 Author. Mem. d. 1. Soc. Zoologique de France, Tome vi. annee 1893, p. 57. Fig. 23. 



disposed on the sides of a long axis, and the mouth is directed 

 alternately towards one and the other end of the axis, but the 



19—2 



