74 BULLETIN 71, UNITED STATES NATIONAL MUSEUM. 



one another, five chambers making a cycle, therefore quinqueloculine, 

 followed by another series added in planes 120° from one another, 

 three chambers making a cycle, these in turn followed in adult 

 Biloculina by chambers in two planes 180° apart and two chambers 

 making the whole cycle. This, then, is the full life history in the 

 complete series shown in the microspheric form (1) proloculum, 

 (2) Cornuspira-\ike chamber, (3) a series of quinqueloculine chambers, 

 (4) a series of triloculine chambers, and in the adult (5) a series of 

 biloculine chambers. 



As the adult conditions are arrived at early in the megalospheric 

 form, and as that is much the more common in usual bottom sam- 

 ples, the early stages of the microspheric form, which in the young 

 might be confused with species of Quinqueloculina or Triloculina, are 

 relatively rare. (See pi. 27, fig. 1.) 



From the standpoint of phylogenetic work it is interesting to note 

 that the early quinqueloculine stage has an elongate aperture with a 

 simple tooth like typical Quinqueloculina, the later triloculine stage 

 a bifid tooth like typical Triloculina, and the adult develops the typ- 

 ical broad aperture and complex tooth of the genus Biloculina. 



BILOCULINA DEPRESSA d'Orbigny. 



Plate 28, figs. 1, 2. 



Biloculina depressa d'Orbigny, Ann. Sci. Nat., vol. 7, 1826, p. 298, No. 7; 

 Mocleles, No. 91. — H. B. Brady, Rep. Voy. Challenger, Zoology, vol. 9, 

 1884, p. 145, pi. 2, figs. 12, 16, 17; pi. 3, figs. 1, 2.— Goes, Bull. Mus. Comp. 

 Zool., vol. 29, 1896, p. 87.— Bagg, Proc. U. S. Nat. Mus., vol. 34, 1908, p. 117. 



Description. — Test in front view nearly circular, compressed, toward 

 the periphery extending out into a thin carina, median portion 

 rotund, in end view ellipsoid, the edges angled and drawn out into 

 the carina; wall smooth, dull white; aperture broad, without a neck, 

 the tooth at the ventral side wide, extending nearly the whole width 

 of the aperture and in end view nearly filling the opening, leaving the 

 actual aperture but a narrow slit-like opening; at the opposite end of 

 the chamber there is often a slight fold formed by the covering over 

 of the tooth of the previous aperture. 



Diameter, specimens occur which have a diameter of 1.5 mm. 



Distribution. — This is much the most common species of the genus 

 in the North Pacific material that I have examined. It is one of the 

 species more or less characteristic of Globigerina-ooze. The species 

 has been recorded at numerous North Pacific stations by Brady, 

 Goes, Picaglia, and Bagg. These stations range in depth from 104 

 to 3,125 fathoms, only two of them, however, being less than 500 

 fathoms in depth. 



In the Albatross, Nero, and Tuscarora material it has occurred fre- 

 quently, between the Hawaiian Islands and the coast of the United 



