FORAMINIFEEA OF THE NORTH PACIFIC OCEAN. 95 



Instead of the outer wall of these last two chambers continuing the 

 curve of the peripheral wall of the second chamber as in 0. marginalis, 

 Orbiculina, and Peneroplis a tangential direction is taken on as in 

 much later chambers in the other types. The early development in 

 this respect then is more accelerated than hi 0. marginalis. This 

 acceleration continues for 0. duplex may develop an annulus in the 

 eighth chamber instead of in the twentieth as in 0. marginalis. In 

 the early stages there is a single series of apertures in the peripheral 

 wall, but in adult growth two such series are usually present. 



A very interesting and significant fact of the acceleration is shown 

 in the stage at which the megalospheric young are freed from the 

 parent test. In Peneroplis as already noted the young have a pro- 

 loculum and the second Oornuspira-\\kc chamber only when set free. 

 The. young of Orbitolitcs marginalis I have not seen in the parent test, 

 but in 0. duplex the young is usually set free in the stage as shown 

 here, many young at this stage being found in the outer chambers 

 of the parent test and also attached nearby. This is a comparatively 

 much later stage than in Peneroplis and an earlier stage than seen 

 in the next species. 



The specimens from Guam in some cases show a plate-like lateral 

 development across the face of the test on either side. One of these 

 specimens is figured (pi. 39, fig. 1). 



ORBITOLITES COMPLANATA Lamarck. 

 Plate 39, fig. 2. 



"Retepora Musripula minima," Soldani, Testaceographia, vol. 1, pt. 3, 1795, p. 

 242, pi. 167, figs, ss, tt; pi. 168, fig. xx. 



Orhitolites complanata Lamarck, Syst. Anim. sans Vert., 1801, p. 376. — Carpen- 

 ter, Rep. Voy. Challenger, Zoology, vol. 9, 1884, pt. 21, 1S83, p. 29, pi. 5, figs. 

 14-18; pis. 6, 7, 8.— H. B. Brady, Rep. Voy. Challenger, Zoology, vol. 9, 1884, 

 p. 218, pi. 16, figs. 1-6; pi. 17, figs. 1-6. 



Description. — Test in the form of a circular disk, the surfaces 

 distinctly concave toward the center, periphery usually the thickest 

 part of the test, convex in the middle, except the first three chambers 

 all the chambers form annuli, divided into numerous chamberlets 

 both in the circle and laterally so that in an adult specimen there 

 may be three tiers of chamberlets in the annular chamber, an outer 

 series on either side of a thicker central series, those of the outer 

 series not communicating with one another but with the central 

 series; wall nearly smooth; apertures very numerous. 



Diameter, from 1 to 25 mm., the average being well under the 

 medium of tins range. 



Distribution. — Brady records this species from the Loo Choo Is- 

 lands and from the Hawaiian Islands. Bagg also records it from 

 three stations in the latter region Albatross D4000 in 104 to 213 

 fathoms, H4476 in 438 fathoms, and H4566 in 572 fathoms. 



