FORAMINIFERA OF THE NORTH PACIFIC OCEAN. 65 



formed coil usually four chambers required to form the whole volu- 

 tion; aperture without neck or thickened lip, sieve-like, consisting of a 

 circular plate, slightly convex, with numerous pores irregularly 

 arranged. 



Length, averaging about 0.75 mm. 



Distribution. — Type specimen (Cat. No. 9163, U.S.N.M.) from Nero 

 station 2039 in 24 fathoms, off the Hawaiian Islands. It also occurred 

 commonly in material from nearby Nero stations, 2040 in 21 fathoms 

 and 2041 in 33 fathoms. 



The chambers of this species are not compressed and in many of 

 the specimens are slightly more irregular than in the figured specimen. 

 Specimens were common at all three of the above stations, but were 

 not met with elsewhere. Apparently it is a shallow-water tropical 

 species. 



Genus TRILOCULINA d'Orbigny, 1826. 



Triloculina d'Orbigny, Ann. Sci. Nat., vol. 7, 1826, p. 299 (Type T. trigonula 

 (Lamarck)). 



. Description. — Test in its adult development consisting, as seen 

 from the exterior, of three visible chambers added in planes 120° from 

 one another, the third of each series added in the plane of the third 

 preceding and covering it. 



In its development it has been shown that in their microspheric 

 form at least the species of Triloculina have a typical quinqueloculine 

 development which precedes the adult triloculine condition. There- 

 fore the young microspheric specimens of Triloculina may appear to 

 be quinqueloculine and may possibly be mistaken for species of 

 Quinqueloculina except for their association with adult Triloculina 

 or possibly developing specific characters early enough to show their 

 true relationships. 



TRILOCULINA TRIGONULA (Lamarck). 

 Plate 25, fig. 3. 



Miliolites trigonula Lamarck, Ann. du Mus., vol. 5, 1804, p. 351, No. 3; Anim. 



sans Vert., vol. 7, 1822, p. 612, No. 3. 

 Triloculina trigonula d'Orbigny, Ann. Sci. Nat., vol. 7, 1826, p. 299, No. 1, 



pi. 16, figs. 5-9; Modeles, No. 93. 

 Miliolina trigonula Williamson, Rec. Forain. Great Britain, 1858, p. 83, pi. 7, figs. 



180-182.— H. B. Brady, Rep. Voy. Challenger, Zoology, vol. 9, 1884, p. 



164, pi. 3, figs. 14-16. 



Description. — Test in the adult with three visible chambers, 

 smooth, the angles of the chambers rounded, whole test slightly 

 longer than wide, in end view rounded triangular, the sides convex; 

 aperture with a rather broad bifid tooth, the angles in end view 

 rounded, in outline flattened. 



Length usually about 1 mm. 



