FOEAMINIFERA OF THE ATLANTIC OCEAN 19 



the general form of Quinqueloculina is already developed so that from 

 one side four coils are visible and from the opposite side only three. 

 From Quinqueloculina, which has already developed the definite 

 coiling in planes 144° apart and five chambers making a cycle, there 

 are developed a number of genera. Miliola and ScMumhergerina 

 develop a cribrate aperture, but keep the quinqueloculine form. A 

 uniserial form follows the quinqueloculine stage in Articulina, Tuhi- 

 nella, and Nubeculina. In Hauerina and Nummuloculina, a planispiral 

 developraient with several chambers to a coil takes place after the 

 quinqueloculine young, the former with a cribrate aperture. A 

 sigmoid development takes place in Sigmoilina and a planispiral 

 development with but two chambers in a coil following the quinque- 

 loculine stage in Massilina and Spiroloculina. Nearly all of these 

 genera which are derived directly from Quinqueloculina develop 

 species with an arenaceous outer layer above the imperforate 

 calcareous inner layer of the test. The apertural tooth throughout 

 this series is normally a simple one. The microspherie and megalo- 

 spheric forms both show a quinqueloculine stage in the early 

 development in this group. 



In Triloculina there is added to the quinquelocuhne stage a further 

 development in which chambers are added in planes 120° apart and 

 three chambers making a cycle. Species with an arenaceous exterior 

 are developed and the apertural tooth normally has a bifid end. In 

 the megalospheric form the quinqueloculine stage may be skipped even 

 though it appears in the microspheric form of the same species. From 

 Triloculina are developed Trillina with cribrate aperture and laby- 

 rinthic interiors, Flintina which becomes more or less planispiral, and 

 Ptychomiliola in which the last-formed chambers uncoil and tend to 

 become uniserial. 



From Triloculina is added the further development, that of cham- 

 bers added 180° from one another and two chambers making up the • 

 entire exterior of the test. The apertural tooth becomes broad and 

 flat, and an arenaceous exterior is not normally developed in this 

 series. In the microspheric form in section the early stages show 

 quinqueloculine and triloculine stages before the "biloculine" devel- 

 opment is taken on. In the megalospheric form the quinquelocuhne 

 stage is often skipped and in specimens with very large proloculum 

 the triloculine stage may also be wanting. 



From Pyrgo there are several genera developed. In Fahularia, the 

 test becomes labyrinthic and the aperture cribrate. In Flintia, the test 

 becomes spread out so that several chambers are visible from the 

 exterior, the appearance being Hke Spiroloculina, but with the devel- 

 opment from Pyrgo. In Nevillina, Idalina, Periloculina, and Lacazina 

 there are highly specialized genera with the last-formed chamber 



