330 Transactions of tin Society. 



ellenl preservation bul are doubtless fossils, are extremely com- 

 pressed, the relation of their heighl to the breadth being Less than 

 one quarter of the usual dimensions. The typical curve of the 

 chambers is, however, present, as is also the customary radial line 

 of beaded markings on the base, although these arc remarkably 



delicate. 



Ai the present day this species appears to lie confined to the 

 Pacific and Australian seas, where it is often fairly abundant. It 

 i- one of the few species of Foraminifera in which "plastogamy" 

 appears to occur with any frequency, twin specimens being nearly 

 always present in any gathering which contains many specim 

 of the form. It has been recorded from the Eocene of Paris and 

 some later deposits. 



Breadth, ■ 37 mm. Height, • 05 mm. 



371. Discorbina polystomelloides Parker and Jones. 



Discorbina polystomelloides Parker and Jones, 1865, Phil. Trans, vol. civ. 



p. 421, pi. xix. fig. 8. 

 Ditto. (Parker and Jones) Brady, 1884, Foram. ' Challenger,' p. 652, pi. xci. 



fig.l- 

 A few well preserved specimens, all fossil, and, judging from 

 their condition, derived from at least two and perhaps three different 

 deposits. At the present day the species is of fairly common occur- 

 rence in the coral sands of the Australian and Pacific seas. We 

 have no knowledge of any previous occurrence as a fossil, but our 

 specimens are doubtless derived from some of the Tertiary deposits, 

 characterized by tropical and sub-tropical fauna. 



372. Discorbina rosacea d'Orbigny sp. var. Selseyensis var. n. 

 (Plate X. figs. 20,21.) 



We figure a curious little Discorbina which we think should be 

 attributed to this species, or which perhaps may form a link con- 

 necting D. rosacea, D. nitida, and D. orbicularis. Two or three 

 specimens only have been observed, all recent, and all characterized 

 by the same constant features. 



The shell, which seen from above is almost exactly circular in 

 outline, consists of about two or three convolutions of chambers. 

 The shell is dome-shaped on the superior surface, concave below : 

 sutures flush, clear bands of shell-substance as in D. nitida ; the 

 outer margin of the shell presents a similar band of shell-substance. 

 On the inferior side the surface of the chambers is covered with 

 weak corrugations diverging from the central axis of the shell ; 

 texture glassy (hyaline); perforations extremely minute. Apart 

 from the under surface of the shell this variety might readily be 

 mistaken for a dome-shaped specimen of D. nitida, but the mark- 

 ings on the inferior surface are peculiarly distinctive. The tangential 



