FORAMINIFERA OF THE NORTH PACIFIC OCEAN. 



93 



Distribution. — Bagg records this species as not very common at 

 three Albatross stations near the Hawaiian Islands, D4000, in 104 to 

 212 fathoms; H4476, in 438 fathoms; and H4694, in 865 fathoms. 

 I have had the species from the same region from the following sta- 

 tions: Nero, 2037, in 55 fathoms; 2038, in 34 fathoms; 2042, in 55 

 fathoms; 2043, in 58 fathoms; and 2071, in 271 fathoms; from Nero 

 station 1466, in 234 fathoms off Guam, from Alert station 1177, in 

 23 to 118 fathoms, and from Gasper Straits, North Pacific Exploring 

 Expedition, Captain Rodgers. 



Orbitolites marginalis is a species which builds all its chambers, with 

 slight exceptions, in a single plane. As a result a test is formed which 

 when mounted in balsam may be viewed in optical section throughout. 

 Its development is much less accelerated than that of the other species 

 of Orbitolites and its study throws 

 light on obscure points in the devel- 

 opment of the higher, more complex 

 species. 



In figure 47 is shown the young 

 of a megalospheric specimen of 0. 

 marginalis. There is a nearly spheri- 

 cal megalospheric proloculum (1) fol- 

 lowed by an encircling Ctonuspira-like 

 chamber (2) making nearly a single 

 coil. This differs from both Penerop- 

 lis and Orbiculina, which each had a 

 second chamber but half a coil in 

 length. This elongated second cham- 

 ber is also seen in the other species 

 of Orbitolites in the megalospheric form, sometimes being quite a full 

 coil in length. The second chamber is very low at its inception, but 

 gradually increases in height to its apcrtural end. The wall is con- 

 tinuous with that of the proloculum, of uniform thickness with it and 

 builds no floor on the wall of the proloculum. 



Chamber 3 is somewhat ovoid, not the globular form of the third 

 chamber seen in Peneroplis and Orbiculina, but more like later cham- 

 bers in those genera. It has two apertures instead of having a single 

 one, as in the other genera mentioned; chamber 3 in this specimen 

 of O. marginalis may be compared in this respect with the fourth 

 chamber in Orbiculina adunca, with the eighth chamber in Orbiculina 

 compressa or with the sixteenth chamber in the specimen of Peneroplis, 

 figured by Schacko. 



Chambor 4, however, becomes divided into two chamberlets by a 

 median partition which is perforated near the apertural wall so that 

 free communication exists between the chamberlets. The number of 

 chamberlets increases rapidly in the succeeding chambers, as added, 

 and the tenth chamber has nine chamberlets. 



Fig. 47.— Early stages of Orbitolites mar- 

 ginalis, x 50, in optical section. 



