GASTEBOPODA. 315 



PPterodonta, D'Orbigny. 



Type, P. inflata, D'Orbigny. 



Fossil, 8 species. Chalk. France. 



Shell oblong, ventricose, spire elongated ; aperture oval, lip 

 slightly expanded, notched in front, and with a tooth-like ridgo 

 internally, remote from the margin. 



PToENATiXA, A. Adams. 



Type, T. voluta. PI. XIV., Fig. 5. 



Shell cylindrical or fusiform, spire conspicuous, apex sinistral, 

 suture channeled, columella callous, 1 -plaited. 



Animal vnth a broad, trigonal head, rounded in front; ten- 

 tacular lobes triangular, with eyes at their outer bases ; foot 

 short, truncated in front. 



Distribution, 24 species. West Indies, United States, Medi- 

 terranean, Philippines, China, Australia. On sandy bottoms, 

 ranging to 35 fathoms. (Adams.) 



Fossil, 13 species. Tertiary. 



Volvula, Adams (Bulla acuminata, Brug.), is a small con- 

 voluted shell, with the spire concealed, and the columella 

 obsoletely folded ; it is referred to Cylichna by Loven, to 

 Ovulum by Forbes. Distrilution, 12 species. Britain, Medi- 

 terranean, Asia. Fossil, Pliocene — . Suffolk. 



Family II. — Bullid^. / 



Shell glohuLsLY or cylindrical, convoluted, thin, often punctate- 

 striated ; spire small or concealed ; aperture long, rounded and 

 sinuated in front ; lip sharp. No operculum. 



Animal more or less investing the shell; head a flattened 

 disk,* with tentacular lobes, often united ; eyes immersed in the 

 centre of the disk, or wanting ; foot oblong, furnished with a 

 posterior lobe [meta-podium), and side-lobes [epipodia) ; gill 

 single on the right side of the back, covered by the shell; 

 mantle-margin simple or expanded, and enveloping the shell. 

 Lingual dentition very various ; central teeth often wanting, 

 laterals single or numerous. Gizzard armed with calcareous 

 plates. Sexes united. 



♦ The cephalic expansion of the BuUidae is formed by the fusion of the dorsal and 

 oral tentacles. {Cuvier.) Tlie tentacular lobes, or posterior part of the disk, is sup- 

 plied with nerves from the olfactory ganglia ; the anterior poition of the disk receives 

 braiMihes from the labial nerve, which comes from the front margin of the cerebroid. 

 {Hancock.) 



p2 



