220 THE NORTHERN MICROSCOPIST. 
The diagrammatic section and projection of an adult frustule of 
Amphora may be seen in fig. 47. Pin 
It often happens with preparations which have been boiled in 
acid, that the valves have lost their hoops, and are consequently 
found separated from each other. In this case they usually he 
upon the most convex side of the larger flap, so that these may 
PP: cS. aPP: 
Qs 
eit 
Fig. 47. 
g.p. Large flaps (grand pans ) 
p.p. Small flaps (petits pans ) 
c.s. Outer hoop (connectif supérior ) 
c.z, Inner hoop (connectif inférieur ) 
7. Raphe (vaphé) 
a. Central nodule (7odule central) 
often be seen in a more or less oblique position, 1st, a small flap ; 
2nd, the raphe with its three nodules; 3rd, the upper part of a 
large flap ; 4th, a part of the interior surface of the last which pro- 
jects beyond the free edge of the small flap. In other words, we 
see at the same time in this last instance the upper portion of the 
great flap outside the raphe, and a portion of variable and lesser 
breadth of the internal surface of this same flap—a circumstance 
occasionally producing appearances which, at first sight, are some- 
what difficult of interpretation. 
Fig. 48 shows us a case of this kind. When the hoop is at- 
tached to the valve, the view is complicated by the addition of 
lines representing its point of junction with the valve, as well as 
its free edge. 
A little attention is sufficient to unravel all these details, which 
