vii MOLLUSCATHE FOOT AND ITS GLANDS 107 



B. Gastropoda. 



1. Prosobranchia. 



With rare exceptions, which will be described later, the foot, which is well 

 developed in this order, has a simple (undivided) flat sole for creeping. 



Propodium. In a few cases, however, the anterior portion of the foot forms a 

 propodium well marked off from the rest of the organ. This is especially the case 

 in the Monotocardia (Olividce, Harpidcc, certain species of Pyrulidce, Strombidce, 

 Strambus, Pterocera, Tercbellum, Rostellaria [Fig. 6, p. 6], Xenophoridce [Fig. 5, p. 5], 

 Xaricidcc, Naticidce [Fig. 98]). 



Among the above, the propodium is particularly well developed in Oliva, sepa- 

 rated from the rest of the foot by a transverse furrow and forming a semicircular 

 disc. 



In the large foot of Natica (Fig. 98), the propodium is also very distinct. It 

 has an anterior lobe which bends back over the shell, and so covers the head. 



FIG. 98. Natica Josephina, with protruded proboscis, from the right side (after Schiemenz). 

 1, Propodium; 2, sucker-like boring appendage of the proboscis (3) with boring gland; 4, siphon 

 (here formed by the foot) ; 5, tentacle ; 6, lobe of the metapodium, which usually covers a large 

 part of the shell from behind, and carries the operculum on its inner side ; 7, metapodium. 



Sometimes the propodium forms a sort of siphon on the left side, and in other cases 

 the lobe which bends back over the shell shows a bulging. Both these arrangements 

 serve to conduct water to the respiratory cavity. The metapodium also, which, 

 when swollen and expanded, spreads out widely, carries on its dorsal side a lobe 

 which bends forward over the shell, and carries the operculum on the side nearest 

 the shell. 



In most Prosobranchia the metapodium carries, on its dorsal side, a horny or 

 calcareous operculum which serves to close the shell. 



Epipodium. The epipodiuin is very commonly present in the Diotocardia. It 

 is most strongly developed in Haliotis (Fig. 105, p. 121), where it surrounds the base 

 of the foot in the form of a large integumental fold. This fold, which may aptly 

 be called the ruff, has fringed or digitate appendages as well as long contractile 

 tentacular processes. The tentacles here, as in other Prosobranchia, are organs of 

 touch, and may be provided at their bases with so-called lateral organs. In the 

 Fissurellidce this epipodial ruff is replaced by a row of numerous tentacles or 

 papillae, rising on each side from the base of the groove between the base of the foot 

 and the visceral dome. Among the other Diotocardia also, the epipodium is well 



