
No. 464.) STAGES IN LAGENIDE 545 
angle in the angle of curvature if it may be so called. In the 
entire development from the right-angled condition in the Nodo- 
sarian young, there is a change gradually to an acute, then a 
right, next an obtuse, and finally back to the right angle again. 
This then represents the mechanics of the uncoiling. The char- 
acter of uncoiling in these four species of Cristellaria is repre- 
sented in Figs. 9-12, in which the black chambers represent the 
portion showing senescent uncoiling. The white portion shows 
the extent of the coiled development. 
Marginulina.— The first three chambers in the specimen of 
Marginulina figured (Pl. ı, Fig. 4), are exactly comparable to 
the same chambers of Cristellaria (Pl. 1, Fig. 8). The first 
chamber is Lagena-like, the addition of the second gives the 
oblique Nodosarian form, and the third is seen to be truly 
Cristellarian. The formula thus far would be as in the pre- 
ceding, L+N+C. The fourth and fifth chambers in this spec- 
imen of Marginulina, however, present a new feature; they fail 
to extend back to the initial 
one, but strike off at a tangent 
showing the incipient stage of 
uncoiling. The chambers as 
built, continuing in the line 
or direction initiated by the 
fourth chamber, form a Nodo- 
sarian growth and the adult 
A 

therefore may be represented 
by the formula, Marginulina 
mis + N+ C +N... Thisis 
shown in Fig. 14 in section, 
and in Fig. 13 from the ex- 
Fic, i Marginulina ensis Reuss, showing terior. 
the main portion of the growth uncoiled. In certain cases in old age 
Mud d m roh median line of the last-formed chamber is 
less closely overlapping than 
the preceding and therefore takes on a form very much like 
Lagena. In Marginulina, representing this last chamber in the 
formula we have, Marginulina = L+N+C+N+L. This shows 
a complete cycle of stages seen in progressive and typical sen- 


