FORAMINIFERA OF THE NORTH PACIFIC OCEAN. 83 



mens are from Nero station 461 in 711 fathoms and 1692 in 754 

 fathoms between Midway Island and Guam. 



This is a rather striking species with its large spines and projecting 

 neck. It is named after Dr. James M. Flint, of the United States 

 National Museum. 



Genus NEVILLINA Sidebottom, 1905. 



Nevillina Sidebottom (Type N. coronata (Millett)), Mem. and Proc. Manchester 

 Lit. and Philos. Soc., vol. 49, pt. 2, No. 11, 1905, p. 1. 



Description. — "Test free, elongate, more or less pyriform, circular 

 in transverse section, the final chamber completely embracing the 

 previous one. Aperture circular, complex, formed by numerous in- 

 curved lamellae, meeting centrally." 



The above is the original description of the genus as given by 

 Sidebottom. The early stages are shown in his figures to be trilocu- 

 line before the final single chambered condition is taken on. Evi- 

 dently this is a genus which is developed from Biloculina and is found 

 in a region containing older types such as Trigonia and Nautilus. 

 Comparing the fossil foraminifera, the relationships of this most inter- 

 esting form are rather clearly indicated. 



Munier-Chalmas and Schlumberger have described two genera, 

 Idalina and Periloculina, from the Upper Cretaceous of southern 

 Europe, which are very clearly related to this genus Nevillina. In 

 both Idalina and Periloculina the same character of a completely 

 embracing chamber is found in the adult and the aperture is also 

 complex, in both having a large area with many openings radiating 

 toward the center. In Idalina especially is found a circular aperture 

 with numerous roughly triangular openings with the base at the 

 periphery and apex toward the center, rather more ornate and com- 

 plex than in Nevillina, but essentially the same. 



The development of both Idalina and Periloculina has been worked 

 out by Munier-Chalmas and Schlumberger in great detail. 



In the development of Idalina, at least in the microspheric form, 

 after a Cornuspira stage following the proloculum, there is developed 

 the regular quinqueloculine test with a 2/5 arrangement of the cham- 

 bers — that is, each succeeding chamber placed at a point 144° from 

 the preceding one, five chambers being necessary to make up the 

 periphery. This in turn is followed by a regular triloculine stage, in 

 which the chambers are added 120° from one another, three chambers 

 completing the periphery, followed in turn by a biloculine stage with 

 chambers 180° from one another, two chambers completing the 

 periphery. In the final adult stage the last formed chamber embraces 

 all the others, except at the point of attachment above the previous 

 aperture. The development of Periloculina shows the same series of 

 stages in the microspheric form at least. 



