20 



BULLETIN" 71, UNITED STATES NATIONAL MUSEUM. 



opment in the quinqueloculine group is shown. Molina antiqua 

 Munier-Chalmas and Schlumberger occurs in the two forms, one with 

 a microspheric, the other with a megalospheric proloculum. The 

 figures used are taken from those of the two authors mentioned. 

 The development of a specimen with a microspheric proloculum is 

 shown in figure 26. There is a globular proloculum followed by a 

 short Cornuspira-likc chamber as the second stage in development. 

 Following the second, chambers 3 to 23, inclusive, are arranged on 

 a quinqueloculine plan of chambers in radial planes 144° from one 

 another. This relation of the chambers is not always apparent from 

 the position of the successive chambers, as there may be a consid- 

 erable departure from the typical angle in individual chambers, 



but the average of the 

 angles of the planes 

 during tins quinqueloc- 

 uline stage is always 

 close to 144°. 



Two sections figured 

 by Schlumberger were 

 measured as to the 

 angles between suc- 

 cessive chambers dur- 

 ing the quinquelocu- 

 line stage. In one case 

 the average of 11 an- 

 gles was 137°; in the 

 other the average of 

 eight angles was 142°. 

 While these early 

 chambers were not as 

 uniformly arranged as 

 in adult Quinquelocu- 

 lina, the average is 

 very close. Following 

 the quinqueloculine stage chambers are developed, arranged on a triloc- 

 uline plan, the chambers added in radial planes 120° from one another. 

 In the larger figure chamber 24 is 115° from the plane of chamber 23; 

 chamber 25 is 130° from the plane of chamber 24 — an average of 

 122.5° for these two chambers. In another section of Molina two 

 chambers in a similar situation gave 124° and 123°, respectively. 



Following the triloculine stage the angle of the planes of addi- 

 tion increase until 180° is attained. There is usually one chamber 

 which bridges over this gap between 120° and 180°, or between the 

 triloculine and biloculine stages, the chamber not fully referable to 

 either plan. In figure 26, for example, the angle between chambers 



Fig. 26.— Section of a microspheric specimen of Idalina anti- 

 qua. X 25 (after Munier-Chalmas and Schlumberger). Early 



QUINQUELOCULINE STAGE, CHAMBERS 3-23 SHOWN IN DARK SHADING, 

 TRILOCULINE STAGE, 24-20, UNSHADED; BILOCULINE STAGE, 27-30, 

 IN LIGHT SHADING; UNILOCULINE STAGE, 31, 32, UNSHADED. 



