FORAMINIFERA OF THE NORTH PACIFIC OCEAN. 



side (fig. la) the width of the tube increases from its inception until 

 the broadest part is developed near the distal end. Seen in vertical 

 view this tube has a nearly uniform width. In cross section (fig. lb) 

 the various parts of the tube are 

 seen to have a considerable dif- 

 ference in height. The proximal 

 portion is low and flattened, the 

 side adjacent to the proloculum 

 being nearly flat, the outer side 

 convex. The height of the tube 

 increases from this point toward 

 the distal end, where its height 

 may equal the width. The aper- 

 ture is contracted and consid- 

 erably smaller than the diameter 

 of the tube. The length of this 

 second chamber is rather con- 

 stant, being usually between a 

 half and a complete coil. 



Another character of especial 

 importance when comparison is 

 made with the early chambers 

 of adult tests is that of the wall. 

 The wall wliich forms the com- 

 mon boundary between the proloculum and the second chamber is, 

 as far as can be determined, a single wall, no new shell substance 

 apparently being laid down by the animal on the floor of the tubular 



chamber. As a result of the walls of the 

 test in its "embryonic" stage are single 

 and of practically uniform thickness. The 

 only exception is the thickening which 

 appears at the aperture of the second 

 chamber. This foreshadows the thickened 

 lip seen in so many of the genera in this 

 family. 



Development of Cornuspira. — In Corn- 

 uspira, which is the simplest of any of the 

 family in its development (possibly ex- 

 cepting Squamulina or Nubccularia, which 

 are degenerate forms), has in reality noth- 

 ing in addition to the developmental char- 

 acters seen in "embryonic" young already 

 described. It has a globular or ovoid pro- 

 loculum followed by a second chamber of indefinite length built on the 

 outside of the previous portion of the test in a planospiral manner 



Fig. 2. — Cornuspira involvens Reuss. ^< 63. Mi- 

 crosphere SPECIMEN VIEWED BY TRANSMITTED 



light. Specimen with very small proloculum, 

 but with its numerous coils growing to a much 

 larger size than the megalospheric form with 

 its much larger proloculum and fewer coils 



(FIG. 3). 



Fig. 3. — CORNUSPIRA INVOLVENS 



Reuss. X63. Megalospheric 

 specimen viewed by transmitted 

 light. Proloculum very- large 

 in comparison with fig. 1, but 

 coils fewer and completed test 

 smaller in diameter. 



