Foraminifera //-om the Coast of Nonuay. 283 



5. Polymorphina communis, D'Orb. 

 PI. X. figs. 25, 26, 27 ; PI. XL figs, 30-34. 



PolymorpMna {Guttulina) communis, D'Orb. Ann. Sc. Nat. vii. p. 266. 

 no. 15. pi. 12. figs. 1-4; Modeles*, no. 62. 



Figs. 30 and 31 (PI. XL) exhibit an early condition of Poly- 

 morj)hina, in which we see an Entosalenia, slightly modified, 

 playing the part of the primordial chamber of this form. This 

 Entosalenian condition of Polymorphina is nearly always appa- 

 rent in specimens sufiiciently small or uuadvanced to leave the 

 early chambers translucent and open to examination. The ex- 

 ceptions to this are chiefly individuals in which the aperture is 

 lengthened outwards and produced into an irregular, ramified, 

 or stag-horn system of tubes; and here, as in those Entosa- 

 lenice in which the aperture is externally tubular, the inner tube 

 becomes obsolete. As they advance in growth, the individual 

 Polymorphinm are invested with additional chambers after a type 

 peculiar to themselves, but in a very irregular manner as regards 

 the capacity and shape of the chambers. The typical arrange- 

 ment of the chambers is best shown in fig. 25. PI. X. (P. ovata, 

 D^Orb. Vien. Forain. pi. 13. fig. 1), in which they are seen to be 

 set-on angularly and alternately (not quite equally on the two 

 flatter surfaces of the shell), pointing backwards and outwards 

 at an acute angle with the axis of the shell, the later chambers 

 considerably overlapping the earlier ones : in this case they com- 

 pose a compressed ovate shell ; but other and innumerable varie- 

 ties in the form and relative size of the chambers result, on the 

 one hand, in the production of short, globular forms, like fig. 32. 

 PL XL [Polymorphina gibba, D'Orb.), and, on the other, of nar- 

 row, elongate shells, like fig. 33 ( Venniculum lacteum, Montagu ; 

 Arethusa lactea, Fleming; P. compressa, D'Orb.). The inter- 

 mediate forms so gradually pass one into the other, scarcely two 

 individuals being identically alike, that it is impossible to regard 

 the extreme forms here indicated (as well as many others, both 

 smooth and ornamented, figured by authors under the names of 

 Polymorphina, Guttulina, and Globulina) as really belonging to 

 more than one specific type. 



The " stag-horn" condition of the aperture (or, rather, the 

 permanent calcareous tubing of the chief pseudopodia) occurs 

 very frequently t; it has supplied some authors with materials 



* By comparing the models, nos. 23, 29, 30, 61, 62, and 63, a good idea 

 may be formed of the variations in the development of the chambers in this 

 species. See also plates 12, 13, and 14 of D'Orbigny's Foram. Foss. 

 Vienne. 



t Soldaui, Testae, ct Zoophyt. pi. 109, 110, HI. 



