FORAMINIFERA OF THE NORTH PACIFIC OCEAN. 



11 



built without filling in the intermediate space between the neck and 

 the body of the test. On the basis of this structure a series of per- 

 forations occur in the adult test along the long axis at regular in- 

 tervals. 



Another group of Eocene S piroloculinae may be represented by 

 S. alata Terquem (fig. 9). In this species the second chamber is 

 shorter than in the preceding (S. bicarinata) , being somewhat less 

 than a half coil in length. The third chamber therefore begins ear- 

 lier and it also is much shorter than in S. bicarinata, being but little 

 more than a half coil in length. As a 

 result, the fourth chamber which initiates ...•:!:? 



the complete generic characters begins at W§&£ '■ 



a point a very little more than one coil 

 beyond the apertural opening of the pro- 

 loculum. 



Other forms which have been usually 

 grouped as Spiroloculina. have a very dif- 

 ferent early development and will be con- 

 sidered after Quinqueloculina is taken up. 



Derivations from Spiroloculina. — In the 

 fossil forms especially there is a consider- 

 able development from Spiroloculina as a 

 base. Uniserial developments take place 

 in species usually assigned to Articulina 

 but apparently do not belong to that genus. 

 Another development is that seen in Renu- 

 lina (figs. 10, 11) from the Eocene of the 

 Paris Basin. Here is a genus apparently 

 limited to the Eocene of the Paris Basin 

 is a foraminifer, which in its general form 

 is very like certain stages seen in the 

 Peneroplis group, in Orbiculina compressa 

 and Orbitolites marginalis. This form of 

 test developed similarly in the various 

 genera gives an excellent example of the 

 parallelism that occurs in the foraminifer a 



development is different and the chambers differ internally even while 

 exteriorly the same general form is developed. 



The first four chambers of a specimen of Renulina are shown in 

 figure 10. There is an oval proloculum (1) followed by a very short 

 second chamber (2), shorter than that seen in any of the genera so 

 far considered. This is but a quarter coil in length. Its wall is con- 

 tinuous with that of the proloculum and of the same thickness. It 

 builds no floor on the surface of the proloculum. The third chamber 

 (3) is long, making with the second chamber a complete coil. The 



Fig. 9.— Spiroloculina alata Ter- 

 quem. X400. Eocene of Vandan- 

 couet, Paris Basin. Specimen 

 showing the early chambers 

 viewed by transmitted light. (1) 

 Proloculum, (2) second cornu- 

 spiralike chamber, (3-5) chambers 

 showing the typical half coil 



LENGTH. 



In these cases the early 



