FORAMINIFERA OF NORTH PACIFIC OCEAN. 



75 



There seems to be no great doubt that Ammodiscus tenuis H. B. 

 Brady is the megalospheric form of the species of which A. incertus 

 (d'Orbigny) is the micro- 

 spheric form. From one sta- 

 tion, Albatross D3431, there 

 were 129 specimens, 26 of 

 which were microspheric (A. 

 incertus) and 103 megalo- 

 spheric (A. tenuis) ; at station 

 D3738, of 16 specimens, 2 

 were microspheric. At sta- 

 tion D4337, 19 out of 30 

 specimens were microspheric. 

 At several other stations both 

 forms were obtained, but the 

 amount of material did not 

 admit of a large series being 

 selected. In general, the meg- 

 alospheric form is the more 

 common, the usual feature 

 wherever series of the two 

 forms have been studied in 

 other genera. Also the micro- 

 spheric form is usually much 

 larger than the megalospheric 

 when the entire growth is fin- 

 ished. This also seems to be 

 the general rule in the other 

 Foraminifera observed from 

 this standpoint. 



AMMODISCUS EXSERTUS, 

 new species. 



Description. — Test consist- 

 ing of a proloculum and long 

 undivided tubular chamber 

 closely coiled for several rev- 

 olutions, then uncoiling, but 

 wall finely arenaceous, with a 

 end of the uncoiled portion, a 



Diameter 0.45 mm. 



Figs. 95-9G.— Ammodiscus incertus. X 20. 95, large 



FORM WITH MICROSPnERIC PROLOCULUM AND MANY 

 SMALL EARLY COILS. 90 a, FORM WITH MEGALOSPHERIC 

 PROLOCULUM, MADE UP OF A FEW LARGE COILS, THE A. 



tenuis H. B. Brady which is the megalospheric 

 formof a. incertus (d'Orbigny); b, apertural view 

 of same specimen showing the megalospheric PROLO- 

 CULUM OF GREATER DIAMETER THAN THE SUCCEEDING 

 PORTIONS OF THE TEST. 



in the same plane, by a straight tube, 

 reddish-brown cement, aperture at the 

 circular opening slightly constricted. 



