484 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



Orbiculina adunca — Material examined. 



Genus ORBITOLITES Lamarck. 



ORBITOLITES MARGINALIS (Lamarck). 



Orhulites marginalis Lamaeck, Hist. Nat. Anim. sans Vert., vol. 2, 1816, p. 196, 



No. 1. 

 Orbitolites marginalis Carpenter, Pliilos. Trans., 1856, p. 192, pi. 9, figs. 1-4. — 



H. B. Brady, Rep. Voy. Challenger, Zoology, vol. 9, 1884, p. 214, pi. 15, figs. 



1-5.— CusHMAN, Bulf 71, U. S. Nat. Mus., pt. 6, 1915, p. 92, pi. 38, figs. 1, 2. 



In the reference last referred to I have figured and described the 

 young stages of the three common species of Oriitolites. Heron- 

 Allen and Earland in their paper, "The Kerimba Archipelago Fora- 

 minifera," note the difficulties of distinguishing this species and the 

 follovkdng (0. duplex) simply on the basis of the single or double 

 series of marginal pores. The same holds true of the Philippine 

 material, where both species often occur together in various stages 

 of development. In such cases the early development is a much 

 more accurate character to distinguish the species, especially in the 

 megalosplieric form. As noted in the above reference on the North 

 Pacific, 0. marginalis has a series of several Orbiculine chambers with 

 single apertures and before divisions occur in the chambers has 

 developed to a decidedly crozier-shaped test. Before true annular 

 chambers are developed the test attains a considerable size. Through- 

 out the test there is a single layer of chambers unless toward the edge 

 there may be a tendency toward 0. duplex and a double series of 

 pores developed. 



0. duplex, on the other hand, has a much more accelerated develop- 

 ment as there figured, and the crozier-shape is attained almost at once 

 and annular chambers are developed very early. The double tier of 

 chambers also is developed early, but their apertures may for some 

 time all be in a single series in the middle of the border. 



As also noted by Heron- Allen and Earland, 0. duplex is much more 

 prone to exhibit excess developments of shell material in the form of 

 extra plates than 0. marginalis. 



Where living material was preserved all three species show a decided 

 greenish color, due to the presence of symbyotic algae. These were 

 perhaps most marked in 0. complanata. 



