40 DE. CAEPENTEE'S EESEAECHES ON THE FOEAMINIFEEA. 



most convolution of a young Operculina, and affording a most advantageous 

 display of its canal-system : a a, marginal cord of the inner convolution ; 

 b b, b b, spiral lamina of the outer convolution ; c c, c c, spiral canals ; d d, d d, 

 origins of the interseptal canals from the spiral canals; e, e, e, projection of 

 the septal bands of non-tubular shell-substance into ridges on the surface : 

 120 diam. 



Fig. 13. Portion of the marginal cord, a, a, of Operculina, as seen in a section passing 

 through the median plane, showing the fusiform spaces formed by the inoscu- 

 lation of the canals: 120 diam. 



Fig. 14. Another portion, showing more elongated and less regular spaces : 120 diam. 



Fig. 15. Transverse section of the marginal cord, aa, as seen in a vertical section of 

 Operculina (fig. 8), showing its slightly furrowed external surface, the canal- 

 system which traverses its interior, its junction with the ordinary tubular 

 substance, bb, of the spiral lamina, and the spiral canals, cc: 120 diam. 



Fig. 16. A similar section from another specimen, showing deep furrows upon the 

 external surface of the marginal cord : 120 diam. 



PLATE V. 



Fig. 1. Side view of an Operculina, of which a portion of the last whorl has apparently 

 been broken off, and the injury repaired by the continuation of the marginal 

 cord along the line of fracture: 10 diam. 



Fig. 2. Portion of the outermost and penultimate convolutions of Operculina, laid open 

 by vertical fracture : a, external surface of marginal cord of the convolution 

 inclosed by them ; a', a', transverse sections of the marginal cord in the outer 

 convolutions ; b b, the two marginal canals, whose transverse sections, b' b', are 

 seen in the penultimate convolution ; c, septum between the contiguous 

 chambers of the penultimate convolution ; c 1 , the same in the outer convo- 

 lution ; d d, origins of interseptal system of canals ; e, e, fissures of communi- 

 cation between contiguous chambers ; f, secondary pores ; g g, thick spiral 

 lamina of tubular substance, formed by the coalescence of that g' g' of the 

 last whorl over that of the penultimate whorl : 75 diam. 



Fig. 3. Side view of an Operculina, of which the last whorl has closed in by a gradual 

 diminution in the size of its chambers: 10 diam.. 



Figs. 4, 5. Fjxternal surface of marginal cord, a a, showing two modes of disposition 

 of its furrows, in which are seen the orifices of some of the canals ; at a' a! the 

 cord is seen in transverse section ; and at b b is shown its junction with the 

 spiral lamina : 75 diam. 



Figs. 6 to 8, 10 to 12. Varieties in the superficial characters of Operculina: 40 diam. 



Fig. 9. Young specimen of the tuberculated variety of Operculina, showing an extra- 

 ordinary development of the central clusters of tubercles: 10 diam. 



Figs. 13 to 17. Successive stages of growth of Amphisteyina Cumingii: 10 diam. 



