FORAMINIFERA OF THE NORTH PACIFIC OCEAN". 



13 



Fig. 12. — Quinque- 

 loculina suborbic 

 ularis d'orbigny. 

 Section of young. 



X 300 (ADAPTED 

 FROM SCHLUMBER- 

 GER). P. PROLOCU- 

 LUM. 



In Quinqueloculina there is an oval proloculum varying in size in 

 the two forms of the species, microspheric and megalospheric, as 

 already noted. It is followed by an elongate chamber about half a 

 coil in length, closely coiled about one side of the proloculum, and 

 builds no floor. The wall of this second Cornus2)ira-\ike chamber is 

 of the same thickness and continues with the proloculum. 



A longitudinal section of the first two chambers of Quinqueloculina 

 suborbicularis is shown in figure 12. This is of the same abbreviated 

 Cornuspira-like type as the second chamber in vari- 

 ous other genera already described. 



The early development in Quinqueloculina rugosa 

 d'Orbigny is shown in figure 13. The proloculum is 

 circular in cross section and the second Cornuspira-like 

 chamber being cut twice is shown on opposite sides of 

 the proloculum at 2 and 2a. The third chamber, 

 shown in cross section at 3, builds no floor, a character 

 usually noted in this genus. Its outline in cross sec- 

 tion is rounded and smooth. Its length, as is that of 

 the succeeding chambers, is a half coil. Chamber 4 is 

 added in another plane 144° of an arc from the posi- 

 tion of its predecessor, chamber 3. Chamber 5 is 

 added in a plane 144° from chamber 4, and so on for the sixth and 

 seventh chambers. With the seventh chamber the generic character 

 is attained, that of a test with five chambers visible from the exterior. 

 Additional chambers are seen in figure 15. Chamber 8 is added in the 

 same plane as chamber 3 and covers it; chamber 9 in the same plane as 

 chamber 4, and so on. Succeeding chambers are added in planes 

 144° from one another, but the five planes in any one cycle are de- 

 veloped 72° of an arc from one another. This 

 is similar in a general way to a 2/5 arrange- 

 ment in the phyllotaxy of plants where suc- 

 ceeding leaves are developed 144° from one 

 another, but the whole cycle of five leaves is 

 made up of a series of radial planes 72° apart. 

 In the vertical axis two and a half revolutions 

 are made by five chambers, as each is a half 

 coil in length, while in the horizontal axis two 

 cycles are made before a chamber is added 

 directly in the same plane as the last of the preceding series. In typical 

 Quinqueloculina, then, after the seventh chamber each chamber is 

 added directly outside its fifth preceding chamber. In Quinqueloculina 

 the generic character is completed with this development, and in 

 further growth simply an increase in size results from the addition 

 of new chambers in this same series of planes. This character will 

 be called " quinqueloculine " when seen in the young of other genera. 

 In various species of Quinqueloculina there is a progressive devel- 

 opment in the ornamentation, the earlier formed chambers being 



Fig. 13.— Early chambers of 

 Quinqueloculina rugosa 

 d'Orbigny. X 300 (adapted 

 from Schlumberger). 



