43 
** Gills enclosed, in one or three comb-like lines on inner side of 
mantle- cavity. 
Fam. 34. Lirrorrnip#. Mantle edge simple or with only a 
slight fold in front; gills in two series; shell free; foot flat (figs. 
20, 21). Assiminia, Littorina, Risella, Pagodus, Modulus, &c. 
Fig. 21.—Littorina littorea. 
Fam. 35. Puanaxtp2. Mantle edge with a siphon and shell with 
a notch in front; teeth 3-1-3, inner broad, two outer lmear. Pla- 
naxis, Quoyia, ’Litiopa. 
Fam. 36. MeLantap&. Mantle edge torn, with a more or less 
distinct siphon in front ; gill of a single series of plates (figs. 22, 23). 
Rissoa, Skenea, Melania, Melanopsis, Vibex, Faunus, Melanatria, 
Rhinoclavis, Cerithium, Telescopium, Triphoris, Terebellum. 
Fig. 23.—Melanopsis buccinoides. 
Fam. 37. Vermetip#&. Shell attached, irregular; foot scarcely 
fit for walking, dilated, clavate at the end. Vermetus, Serpuloides, 
Siliquaria, &c. 
Fam. 38. ?Vanicororp&. Shell free; foot small, circular, pro- 
duced in front, with a dilated membranous expansion on each side ; 
operculum horny, ovate; teeth ——? Vanicoro. 
