442 



MANUAL OF THE MOLLTISCA. 



is seldom compact, its lamellae are extremely thin, and sepzjcatod 

 by intervals like the water-chambers of Spondylus ; similar 

 spaces occur in the deposit, filling the icnbonal cavity of the 

 long-beaked oysters.* 



The inner layer ceases at the pallial line, beyond which., on 

 the rim of the shell, the cellular structure is often apparent ; 



Fig. 231. Section of a fragment of Ostrea CornucopicB. 



obscure bifurcating impressions radiate from the pallial line to 

 the outer margin (Fig. 232, v, v). 



These have been compared to the vascular impressions of 



Fig. 232. Part of the rim of Badiolites Mortoni, Mantell.t 



Crania (Figs. 193, 194), and constitute the only argument for 

 supposing the Budistes to have been palliohranchiate ; but they 



* The vrater-chambers in some of the cylindrical Hippiuites are large and regular^ 

 like those of the fcsil corals Amplexus and CyatJiophyUum. A section of Hippuritea 

 bi-oculatus passing tlnough only one of the dental sockets, resembles an Orthoceras 

 with a lateral sip}iuu...le ; whilst a Capnnella (Fig. 246), which has lost its outer layer, 

 mi^htbe mistaken for an Ammonite. 



t Traced from the original specimen in the Museum of the School of Mines, b, ia 

 the mner edge ; a, tlie outer edge ; v, v, the dirhotomons impressions ; the horizontal 

 laminae are seen on the shaded side. Lower chalk ; Sussex. 



