12 



BULLETIN 71, UNITED STATES NATIONAL MUSEUM. 



Fig. 10. — First four chambers of a speci- 

 men of Renulina from the Eocene of 

 the Paris Basin. X 160. 



fourth chamber (4) is short, one third of a coil in length, increasing 

 considerably in height at the apertural end while there is a thickened 

 flaring lip. Chambers 5 and 6 (fig. 11) are also a third of a coil 

 in length, maldng one complete coil with chamber 4. The seventh 



chamber is similar. At this stage it is 

 a closely coiled non-involute test, build- 

 ing the later chambers one-third of a 

 coil in length. 



Chamber 8 is very short in compari- 

 son with the preceding ones. Chamber 

 9 is also short but very much higher 

 than earlier chambers, the outer wall 

 taking a tangential direction. This 

 tangential direction of the outer wall 

 is continued in succeeding chambers, 

 greatly increasing the height of the 

 chambers which in all cases continue 

 around to the preceding coil. This 

 makes the form of test noted in forms of Peneroplis, Orbiculina, and 

 Orbitolites, as already noted. This is brought about in the same 

 mechanical way by the similar tangential position of the peripheral wall. 



According to the published figures, 

 in a later stage the chambers may 

 extend back on both sides and form 

 an extended chamber nearly meeting 

 at opposite ends so that if continued 

 slightly an annular growth would re- 

 sult. None of the series of specimens 

 examined had reached this stage. 



Development of Quinqueloculina. — 

 Quinqueloculina and the various 

 genera which are derived from it 

 differ from all the other genera of the 

 Miliolidae in having a plane of coiling 

 which is constantly shifting with each 

 newly added chamber, at least in the 

 young. In all the genera so far con- 

 sidered the test has been planospiral. 



As the genera next to be considered coil in more than one plane, a 

 longitudinal section can not usually be made so as to show the true 

 relation of all the chambers. For the study of these genera, trans- 

 verse sections passing through the proloculum are absolutely essen- 

 tial. The excellent detailed figures given by Schlumberger have 

 been freely drawn upon for the study of these structures. 



Fig. 11.— Complete specimen of Renulina, 

 the early chambers of "WHICH are shown 

 IN FIG. 10. X 13. 



