THE FORAMINIFERA 



109 



of narrow elongated chambers, wound in a planospiral manner 

 about the central chamber in some 7-8 convolutions. The lengths 

 of the several chambers vary from 2 convolutions to \ of a con- 

 volution of the spiral. The arrangement and mode of communi- 

 cation of the chambers recalls the irregular spiroloculine tests of 



/ ; 



FIG. 40. 



Orbitolites tenuissima, Carp. Central region of the specimen represented in Fig. 39. 

 The figure 8 is in the eighth and last convolution of the inner series of chambers. 



X 80. 



Ophthalmidium (Fig. 41). As the five specimens have an approxi- 

 mately similar arrangement, it is probable that the form we are 

 dealing with is megalospheric, though the size of the megalosphere 

 is small. 



When comparing the central regions of 0. marginalis (megalo- 

 spheric) with those of 0. tenuissima, Carpenter regarded the spiral 

 passage of the former as representing " the whole of the original 

 'spiroloculine' coil, drawn up into itself" (p. 24). The difficulty, 

 however, of recognising the long spiroloculine (or Ophthalmidium- 

 like) coil of tenuissima in any of the modifications of the spiral 

 passage met with in the other species of the genus Orbitolites is so 



