ON THE GENUS POLYMORPHINA. 251 
allied genera Polymorphina and Nodosarina. As amongst the Nodosarine (whether 
curved or straight) varieties are found having the chambers so combined that no constric- 
tion marks the course of the septal lines, so in Dimorphina compacta we have an even : 
margin and obscure septation arising from the same habit of growth. The peculiarity of 
contour depending upon the relation of the chambers has been deemed sufficient for 
* specific ” definition in the case of such modifications of Nodosaria, Dentalina, and Vagi- 
nulina; and itis only consistent to distinguish similar Dimorphine by a trivial name. 
For this reason, although the present variety was associated with some of its congeners in 
our partially finished ** Monograph of the Foraminifera of the Crag," under the general 
term Dimorphina tuberosa, we have since regarded it as meeting better the exigencies of 
a scheme of subdivision to distinguish it from the more common form having ventricose 
chambers. 
Distribution.—Dimorphina compacta is of rare occurrence. We know it only as a 
Tertiary fossil, from specimens obtained by Mr. Searles Wood in the rich Cràg deposit at 
Sutton, which has furnished so many rarities. 
DESCRIPTION OF THE PLATES. 
General Note.—The great difference in the size of the various species has rendered it 
impracticable to make the drawings on a uniform scale. The idea of relative size is con- 
veyed by the small vertical line placed near each figure, which represents five times the 
length of the longer diameter of the shell. The actual measurement of average speci- 
mens is given with the descriptions of species. e 
The numbers, 1 to 41, represent “ species ;” the small letters refer to different aspects of 
the same shell, or different specimens of the same “ species.” 
PLATE XXXIX. 
Fig. 1. Polymorphina lactea, Walker and Jacob, sp.: a, copy of Walker and Jacob's original figure 
slightly enlarged ; 5, typical form, after Williamson; c, monstrous double specimen. 
[For sketches of the compressed variety, P. lactea, var. amygdaloides, Reuss, see Woodcuts 
a to d, p. 215.] 
Fig. 2. P. gibba, D'Orbigny : 4 and 5, typi 
D'Orbigny. 
.3. P. gutta, D'Orbigny. Copied from D'Orbigny's figures. 
.4. P. acuminata, D'Orbigny. Copied from D'Orbigny's fig 
a, after Reuss (* Globulina porrecta ^) ; 
cal form ; c and d, compressed variety, P. gibba, var. equalis, 
Fig ure of a Chalk specimen. 
Fig. 5. P. fusiformis, Roemer: b and c, after Bornemann 
(** Guttulina cylindrica cd di 
VOL. XXVII. 
