ORDER I FORAMINIFERA 33 
symmetrically lenticular or discoidal, composed of numerous spirally arranged 
polythalamous volutions, and usually with columnar intermediate skeleton, 
which forms small excrescences on the periphery. The septa and marginal 
OL 
Fig. 37. 
Amphistegina Haueri, VOrb. 
Miocene (Leithakalk) ; Nuss- 
dorf, near Vienna. a, Exterior 

views, enlarged ; 6, Natural Fic. 38. Fic. 39. 
size; ¢c, Median section, ; ; 
greatly enlarged; d, Trans- Operculina complanata, Bast., sp. Miocene ; Heterostegina costata, d’Orb. 
verse section, greatly en- Bordeaux. a, Natural size; b,c, Median and Miocene (Leithakalk); Nuss- 
larged. longitudinal sections, greatly enlarged. dorf, near Vienna. 
cord contain a coarse, anastomosing canal-system, as in Operculina. Primordial 
chamber spherical, sometimes large, sometimes exceedingly minute in size. 
The whorls either merely embrace one another (Assilina) (Fig. 41), or they 
completely envelop one another by means of alar prolongations reaching 
a b c d e 

Fia. 40. 
Nummutlites efr. Lucasanus, Dfr. Eocene; Kressenberg, Upper Bavaria. Several times enlarged. 
a, Marginal cord with canal-system; b, Septal plane with interseptal canal-system; c, Interior of chamber ; 
d, Winely perforate periphery ; e, Small pillars of intermediate skeleton. 
inwards to the centre (Nwmmulona). The septa are pierced in the median 
plane by an oblique slit-like aperture, and also extend into the saddle-shaped 
alar prolongations of the chambers. They are directed in the groups Radiatac 
and Striatae in straight or slightly curved lines (Figs. 40 and 42, (); in the 
Sinuatae they follow meandering courses (Fig. 42, 4); and in the Reticulatae 
(Fig. 42, B) they form an interlacing network by means of connecting pro- 
MOLT D 
