36 DE. CAEPENTEE'S EESEAECHES ON THE FOEAMINIFEEA. 



EXPLANATION OP THE PLATES. 



PLATE I. 



Fig. 1. Ideal figure of Dendritina, partly laid open, so as to show the arrangement of its 

 chambers, the nature of their communications by a single fissure 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 Peneroplis, 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 frequently 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 Operculina, laid open to show the details of its structure : 

 a a a, marginal band (the "spicular cord" of Mr. CARTER, the "bourrelet" of 

 MM. D'ARCHIAC and HAIME), divided transversely at a', so as to show the 

 orifices of its canals, the distribution of which is seen at a"a" 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, c, interior of the chambers of the outer whorl, the alar prolongations 

 of which extend, as shown at c', 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 1 , 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, f, the two spiral canals ; and at 

 g, 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. 



