FORAMINIFEBA OP THE NORTH PACIFIC OCEAN. 97 



constant. At this stage the third chamber is often much contorted 

 as shown in figures 49 to 51, especially marked in figure 51, where the 

 periphery of the third chamber is greatly convoluted as though due 

 to pressure. These young are often very crowded, and when formed 

 the wall must be in a semi-plastic condition before it is hardened to 

 account for the reentrants in the wall such as show in figure 51. The 

 outer rim of chamber 3 has numerous apertures. After the young 

 is set free, it develops chamber 4 as a complete annulus with many 

 chamberlets, comparable to the eighth chamber of 0. duplex or to the 

 twentieth chamber of 0. marginalis showing the great acceleration 

 that has taken place in 0. complanata. From this point it builds 

 annuli throughout further growth, each annulus becoming much 

 divided and having several series of apertures on its peripheral wall. 

 Occasionally specimens of the megalospheric type are found with 

 two prolocula and their accompanying later stages, but finally the two 

 fusing and building as annulus in common, so that in later growth the 

 synthetic test can not be distinguished from an ordinary individual 

 with a single proloculum. This twinned condition is probably due to 

 the closely adjacent position of the attached young when they started 

 their annular growth. As the chambers met the protoplasm must 

 have anastomosed and a common chamber been built. This tends 

 to show the primitive character of the protoplasmic body. 



Genus ALVEOLINA d'Orbigny, 1826. 



Alveolina d'Orbigny, Ann. Sci. Nat., vol. 7, 1826, p. 306 (Type, A. boscii 

 (Defrance)). — H. B. Brady, Rep. Voy. Challenger, Zoology, vol. 9, 1884, 

 p. 221. 



Description. — Test usually elliptical or fusiform, composed in the 

 adult of elongate chambers, each running the entire length of the 

 test, the apertural face of the last formed chamber forming the grow- 

 ing edge of the test; chambers divided into chamberlets with small 

 circular apertures upon the apertural face, at least in the larger 

 species; whole test spirally coiled about the elongate axis. 



This genus seems to be confined to the shallower waters of the 

 Tropics, being a characteristic form in dredgings from about coral 

 reefs. 



ALVEOLINA MELO (Fichtel and Moll). 



Plate 39, fig. 4. 



Nautilus melo Fichtel and Moll, Test. Micr., 1803, p. 118, pi. 24. 

 Alveolina melo D'Orbigny, Ann. Sci. Nat., vol. 7, 1826, p. 306, No. 2.— II. B. 

 Brady, Rep. Voy. Challenger, Zoology, vol. 9, 1884, p. 223, pi. 17, figs. 13-15. 



Description. — Test subspherical or broadly elliptical, coiling on its 

 longitudinal axis, rotaliform at least in the adult; chambers in each 

 whorl few, about eight in number, transversely striate; apertural 

 face forming the growing edge of the test, truncate; apertures numer- 



