FORAMINIFEEA OF THE NORTH PACIFIC OCEAN. 



15 



the cycle. In the figure chamber 3 is in the plane A; chamber 4, 

 144° from it, is in the plane B; chamber 5 in plane C; 6 in plane D; 

 7 in plane E; and 8 again in plane A, overlying chamber 3. 



Derivatives from Quinqueloculina. — The later development from a 

 quinqueloculino form may be seen in the regularly progressive 

 series, Triloculina, Bilo- 

 culina, etc., as will be con- 

 sidered later, but other 

 genera may be consid- 

 ered as direct derivatives 

 from a quinqueloculino 

 stock. These, as in Mas- 

 silina and Hauerina, may 

 add chambers which are 

 planospiral and com- 

 parable to Spiroloculina, 

 except in the young or 

 as in Articulina, where 

 there is developed a uni- 

 serial later development 

 with a quinqueloculine 

 young. The develop- 

 ment of Massilina in the 

 two forms, microspheric 

 and megalospheric, will 

 give a good illustration 

 of a typical derivative 

 from Quinqueloculina. Massilina secans d'Orbigny gives in simple 

 stages the development of characters which make up the genus Mas- 

 silina Schlumberger. From a study of the development of this species 

 it will be seen that this genus is one derived from Quinqueloculina by 



Fig. 1G.— Diagrammatic section of Quinqueloculina. A-E, 

 planes in which chambers are added. 1-9. chambers. 

 Arrows indicate the direction of rotation in the addition 

 of chambers. 



Figs. 17, 18.— Massilina secans (d'Orbigny). 17, Early chambers of microspheric form. X 115. 

 18, complete specimen, x 13 (adapted from Schlumberger). 



the addition of definite differential characters. Both the forms, those 

 with a microspheric and megalospheric proloculum, have been found 

 by Schlumberger. The early chambers of a specimen with a micro- 

 spheric proloculum are shown in figure 17. There is a small pro- 

 loculum followed by the usual ComuspiraAike chamber making a 



