14 



BULLETIN 71, UNITED STATES NATIONAL MUSEUM. 



FIG. 14.— QUINQUELOCULINA UNDULATA D'OEBIGNY. X 150 

 (ADAPTED FROM SCHLUMBERGER). SHOWING PROGRESSIVE IN- 

 CREASE IN ORNAMENTATION, THE NUMBERS OF COSTAE IN- 

 CREASING IN NUMBER WITH NEW CHAMBERS. 



smooth and semi-elliptical in cross section as in the primitive cham- 

 bers seen in the microspheric form throughout the genus. As shown 

 in figure 14, there is a progressive development of ornamentation; 

 in this case an increase in the number of costae from one in chamber 

 3 to a considerable number in chamber 13. In some individuals a 



definite senescent char- 

 acter is shown in the loss 

 of these costae, and the 

 resulting development of 

 smooth chambers like 

 that seen in its own 

 young, the intermediate 

 chambers as seen in sec- 

 tion bearing distinct 

 costae. 



There are both micro- 

 spheric and megalo- 

 spheric individuals de- 

 veloped in Quinquelocu- 

 lina, but they differ only 

 in the size of the pro- 

 loculum and the total number of chambers in the adult, not in the 

 general plan of their development. The fact that the complete 

 stages in development shown by the microspheric form are not dif- 

 ferent from those of the accelerated megalospheric form may be 

 taken as a definite indication that Quinqueloculina is a primitive 

 form at the base of its own 

 series. Succeeding genera dis- 

 cussed show added stages and a 

 dropping out of certain of these 

 in the megalospheric form. 

 Quinqueloculina is considered 

 as the primitive form from 

 which the other genera of the 

 quinqueloculine group have 

 been derived by the addition of 

 differential characters. The 

 proof of this is the fact that 

 they have a quinqueloculine 

 stage in the young of at least 

 their microspheric form. 



In figure 16 is given a diagrammatic figure showing the character 

 of chamber development in a typical Quinqueloculina. The five 

 planes are lettered A to E and the chambers numbered 1 to 9. The 

 arrows indicate the direction of the addition of new chambers in 



Fig. 15.— Quinqueloculina rugosa d'Orbigny. X 



150 (ADAPTED FROM SCHLUMBERGER). SHOWING 

 PROGRESSIVE DEVELOPMENT OF CHARACTERS FROM 

 THE EARLY SMOOTH ROUNDED CHAMBERS TO THE 

 MUCH ANGLED AND PERIPHERALLY EXCAVATED CHAM- 

 BERS OF THE ADULT. 



