104 



THE FORAMINIFERA 



diameters in 108 specimens vary between 49 and 110 /A). The 

 spiral passage almost encircles the megalosphere, and is wider than 

 in 0. marginalis. Though it sometimes communicates with only a 

 single chamber (Fig. 35, A"), there are usually two to five chamber- 

 lets into which it opens directly, by as many apertures (Fig. 35, 

 A and A'), so that the peneropline and orbiculine stages are in such 

 cases abridged, and the annular arrangement speedily attained. 



In a sample of the tests of 0. duplex from Aripo, all (108 in 

 number) were megalospheric. The specimen of the microspheric 

 form above described is from Funafuti in the Pacific. 



PIG. 36. 



Orbitolites complanata, Lamk. The megalospheric (A, ) and microspheric (B, V) forms, 

 whole, and in section, x 5. The primitive disc is seen at the centre of A and a, and young 

 megalospheric individuals (= primitive discs) may be seen at the left-hand end of 6. 



In Orbitolites complanata, Lamk. (cp. p. 73), a much greater degree 

 of complexity is attained, in that the chambers, which in 0. duplex 

 are elongated in a vertical direction, are differentiated into three 

 several layers two layers of superficial chamberlets, one on either 

 face of the test, and an intermediate layer of columnar spaces lying 

 between them (Figs. 36, b, and 38, c). There are here two 

 annular canals corresponding to each annulus of chamberlets, 

 lying at either end of the columnar spaces in the two strata of 

 the test between these and the superficial chamberlets. There 

 are abundant communications between the chamberlets, and those 



