40 
DE. CAEPENTEE’S EESEAECHES ON THE EOEAMINIEEEA. 
most convolution of a young Operculina, and affording a most advantageous 
display of its canal-system : — a marginal cord of the nmer convolution , 
hh, hh, spiral lamina of the outer convolution ; c c, cc, 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, 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 ordinaiy tubular 
substance, bh, of the spiral lamina, and the sphal 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', transverse sections of the marginal cord in the outer 
convolutions ; h 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 ; </, 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 :— -7 5 diam. 
Fig. 3. Side view of an Opefculina^ of which the last whorl has closed in by a gradual 
diminution in the size of its chambers: — 10 diam.. 
Figs. 4, 5. External surface of marginal cord, aa^ showing two modes of disposition 
of its furrows, in which are seen the orifices of some of the canals ; at cdc^ the 
cord is seen in transverse section ; and at 5 5 is shown its junction with the 
spiral lamina : — 7 5 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 Amphistegina Cumingii'. — 10 diam. 
