538 THE AMERICAN NATURALIST. [Vor. XXXIX. 
DEFINITION OF A FEW TERMS. 
The following terms as defined, some of which are new, are 
convenient in the description of the structure of the shell of For- 
aminifera. The suc- 
ceeding divisions of the a 
shellare usually spoken 
of as chambers, the one 
first formed being the 
initial chamber (/ in 
Figs. ı and 2) and the 
last one built in any 
given specimen, the 
anterior chamber (4). 
The initial chamber 
which will be shown 
to have a decidedly 
phylogenetic bearing in 
the group is here given 
a distinctive name — 
the proloculum—to cor- 2 
respond with the term F's- :— Nodosara. Fic. 2 — Uncoiled form of Cristel- 
applied to the embry- Mode: d. anterior en posterior end. Arrows 
onic shell of oth er show the direction of growth ; shaded portions indicate 
the angle of at C, C,/ C" ; S, sutures. 
groups already worked 
out in the Metazoa. The ends of the shell as a whole are called 
anterior (2) and posterior ( P) The walls of the chambers are 
called anterior and posterior walls according to their individual 
position in relation to the direction of growth. The line of 
contact made by the joining of a succeeding to a preceding 
chamber is called a suture (5). In coiled forms the outer bor- 
der formed by the sum of the distal portion of the walls of suc- 
ceeding chambers is called the peripheral margin. The angle 
between the suture and the distal wall of the next succeeding 
chamber in coiled forms is called the angle of curvature for that 
portion of the peripheral margin. These angles are shaded at 
C, C', C", to show the decided differences that the angle may 
assume. 


