Nomenclature of the Foraminifera. 1 81 



structural characters, but also for the bold and masterly exposi- 

 tion of the true philosophical principles on which the zoological 

 relations of this and other species of Foraminifera are to be 

 studied. This ear-shaped Orbiculina adunca is doubtless the 

 typical form, as compared with the further and extreme step in 

 development by the increase and extension of the peripheral 

 chambers, which produces suborbicular discoidal shells, bringing 

 Orbiculina into close parallelism with the typically cyclical Orbi- 

 tolites. The cyclical forms of Orbiculina may be often the result 

 of continued growth of individuals under favourable circum- 

 stances ; but frequently small starved forms quickly take on the 

 cyclical condition, leaving the young sublenticular stage with- 

 out passing through the aduncal. Therefore, in a sense, these 

 may be regarded as varieties. 



Ehrenberg has given good figures of Orb. adunca in Abhand. 

 Akad. Berlin, 1838 (1839), pi. 3. figs. 1 a-ld. 



32. Nautilus Orbiculus. Page 112, pi. 21. figs. a-d. "Recent: 

 Leghorn*." 



This is the thick orbicular, or subnautiloid condition of Orbi- 

 culina adunca, which small and young specimens almost uni- 

 formly exhibit, though some are flatter. The apertural surface 

 is as yet very contracted. 



33. Nautilus angulatus. Page 113, pi. 22. figs. a-e. " Recent : 

 Red Sea." 



In this stage, Orbiculina adunca, still sublenticular, puts on a 

 broader and angular septal face, showing an increase in the 

 space for pseudopodial apertures, which will extend along the 

 marginal area, in the adult shell, for three-fourths of a circle, 

 and around the entire periphery in the cyclical varieties. 



The neat and uniform subdivision of the chambers in Orbi- 

 culina is shown in the three sections given by Fichtel and Moll. 

 We may remark that, not unfrequently, feebly-developed Pene- 

 ropliform varieties, as well as good-sized Adunciform specimens, 

 occur in which the long narrow chambers are at times simple 

 and undivided, being occupied by transversely elongate lobes of 

 sarcode, instead of numerous minute subcubical blocks. 



Orbiculina has its home, as it were, in the West Indies; it 

 occurs also in the Red Sea, the Indian Ocean, and on many 

 coasts of the warmer seas. 



34. Nautilus Melo. Two varieties. Page 118. "Fossil: 

 Brunn in Austria, Kroisbach in Hungary, and other places in 

 Austria and Transylvania." 



Var. a. pi. 24. figs. a-f. Var. /3. pi. 24. figs, g, h. 



* This locality appears strange to us, as we have not, after much seeking, 

 found this shell living in the Mediterranean. Dr. Carpenter, however, 

 quotes it from the JEgean Sea ; it occurs fossil in a white limestone at 

 Corfu; and D'Orbigny figures a minute form (0. Rotella) from the 

 Vienna Tertiaries. 



