336 FORAMINIFERA 



Miogypsininae, early stages distinctly spiral, later growth 

 spiral, which ultimately may become cyclical, or the growth may 

 be largely on only a segment of the periphery producing a test 

 triangular in plan with the embryonic chambers at or near the 

 apex. Lateral chambers well developed. 



OmphalocycMnae, growth cyclical, initially spiral in the 

 microspheric form. Without definitely differentiated lateral 

 chambers; initial chambers, beyond the embryonic, in a single or 

 double layer. If the layer is single it may bifurcate and a third 

 layer may be intercalated between the two previously formed; 

 if it is double there may be direct intercalation of the third 

 layer. 



The features of the embryonic chambers of the megalos- 

 pheric forms are used in defining genera and subgenera, al- 

 though they are subject to considerable variations. Details will 

 be found in the subsequent descriptions. 



There are two hypotheses regarding the origin of the 

 Orbitoididae. According to H. Douville the family is derived 

 from ArnauclieUa or some similar parent and is, therefore, 

 ancestrally related to Camerina. Hofker, however, is of the 

 opinion that the family is derived from ancestors related to his 

 Tinoporidae (Hofker, J., The Foraminifera of the Siboga 

 Expedition, pt. 1, 1927, pp. 4-6) , because of general similarity 

 of structure, including the absence of any canal system. I have 

 restudied many thin sections of orbitoids with Hofker's sugges- 

 tion in mind, and in essentials I am inclined to agree with 

 him. In some of the sections that I have examined there are 

 passages connecting the equatorial with the lateral chambers, 

 similar to the passages between the lateral chambers, as they 

 were figured by Carpenter (Carpenter, W. B., Introduction to 

 the Study of the Foraminifera, pi. 20, fig. 6) . These observations 

 are at variance with Hofker's statement that the median cham- 

 bers communicate with the lateral only by means of pores. I 

 agree with H. Douville in his opinion that Omphalocyclus is a 

 close relative to the orbitoids. Miogypsina and H elicolepidina 

 are also closely akin to the orbitoids. They both lack any canal 

 system and their general structural features are similar to those 

 of the orbitoids. It is probable that Miogypsina is derived from 

 H elicolepidina. My previous expressed opinion of the similarity 



