36 
DE. CAEPENTEE’S EESEAECHES ON THE FOEAMINIEEEA. 
Explanation of the Plates. 
PLATE I. 
Fig. 1. Ideal figure oi Dendritina, partly laid open, so as to show the arrangement of its 
chambers, the nature of their communications by a single fissui-e of irregular 
form (simpler in the earlier whorls, but more complex in the later), the 
overlapping of the earlier whorls by the alar prolongations of the chambers 
of the later, and the manner in which the last turn of the spire tends to 
detach itself from the earlier convolutions. 
Fig. 2. Ideal figure of Penevoplis, partly laid open, so as to show the arrangement of its 
chambers, the nature of their communication by isolated pores, which are 
arranged in a single row in the later whorls, but freQ^uently form a double 
row in the earlier, the rapid increase in the breadth of the spire coincident 
with its very extraordinary flattening in the last convolution, and the very 
slight degree in which the earlier whorls are covered in by the later. 
Fig. 3. Ideal figure of Op^fculind, laid open to show the details of its structure : 
a a a, marginal band (the “spicular cord” of Mr. Caeter, the “bourrelet” of 
MM. d’Aechiac and Haime), divided transversely at a', so as to show the 
orifices of its canals, the distribution of which is seen at in a tangential 
section of the band, and at a!" a'" in a section through the median plane; 
b, b, b, external surface of the chambers, marked out by the septal bands ; 
c, Cy Cy interior of the chambers of the outer whorl, the alar prolongations 
of which extend, as shown at g\ d, over the surface of the interior whorl, 
reaching nearly to the centre of the spire ; the chambers are separated by 
the septa d, d, d, formed by the union of two layers of shell, one belonging 
to each chamber, and having spaces between them in which lie the inter- 
septal canals, whose smaller branches are seen irregularly divided in the septa 
d', d', whilst in the septum d” one of the principal trunks is laid open 
through its whole length ; at the approach of each septum to the marginal 
cord of the preceding whorl is seen the fissure which forms the principal 
connexion between the chambers ; at e, e are seen the secondary orifices of 
communication, and in the same septa is shown the distribution of the inter- 
septal system of canals, branching from f, fy the two spiral canals ; and at 
gy g are seen the conoidal columns of translucent shell-substance, forming 
tubercular projections on the surface, which frequently overlie the septa, and 
are penetrated by branches of the interseptal system of vessels. 
