36 



PEOTOZO A— RHIZOPODA 



PHYLUM I 



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 

 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. 28), or they 

 completely envelop one another by means of alar prolongations reaching 



inwards to the centre (Nwrnnulina). 

 The septa are pierced in the median 

 plane by an oblique slit-like aper- 

 ture, and also extend into the saddle- 

 shaped alar prolongations of the 

 chambers. They are directed in 

 the groups Eadiatae and Stria fae in 

 straight or slightly curved lines 

 (Figs. 27 and 29, C) ; in the 

 Simiafae they follow meandering 

 courses (Fig. 29, A) ; and in the 

 Eeticulatae (Fig. 29, B) they form 

 Pjq 3q an interlacing network by means 



A, Nummnlitic limestone with horizontal sections of oi Connecting prOCeSSCS. The rami- 

 N cUstans Fusch Peyrehorade, in the Pyrenees. B, fications of these lateral prOCeSSCS 

 Nummnlitic limestone showing sections of N. lucasanus _ -i 



Defr. zakophane in the Carpathians. ( Jilet cloisomiaire) may be readily 



seen on fracturing a portion of the 

 test, and are a valuable aid in the determination of species. The oldest 

 Nummulites {N. pristinus Brady) occur very sparsely in the Carboniferous 

 limestone and Upper Jurassic, but are distinguished from the typical later 

 forms by the absence of an interior canal-system in the marginal cord. The 

 typical Nummulites which are so characteristic of the Eocene (Nummnlitic 

 limestone) in Europe, North Africa, Asia and Central America, often build up 

 massive formations. The largest species (iV. gizehensis Ehrbg., N'. orhiculatus 

 Schafh.) attain a diameter of 60 mm. ; the smallest species does not exceed 

 2 mm. ; recent representatives comparatively scarce. 



Subfamily D. Cycloclypeinae Brady. 



I'est flat with a thickened centre, or lens-shaped, consisting of a disc of chambers 

 arranged in concentric annuli with peripheral thickenings, septa double with inter- 

 septal canals. 



OrUtoides d'Orb. (Hymenocyclus Bronn ; Lycophrys Monti.) (Fig. 31). Test 

 discoidal, with circular or stellate contour, often bent, exterior smooth or with 

 radial striae, and composed of numerous concentric annuli disposed about a 

 primordial spiral of three to five whorls. The rings are divided by transverse 

 partitions into small rectangular chambers, and the septa and marginal cord 

 are traversed by canals. Superimposed over the median series of principal 

 chambers on both sides are several layers of flattened secondary chamberlets, 

 which are likewise disposed in concentric rings. Very abundant in the Eocene, 

 associated with Nummulites ; rare in Upper Cretaceous and Miocene. 



Cycloclypeus Carp. Miocene and Recent. 



