THE GASTROPODA 



169 



spire. Genera Bulla, Linnaeus; British. Haminea, Leach; British 

 (Fig. 98). FAMILY 6. ACERATIDAE, Pilsbry. Cephalic shield continuous 

 with the neck ; twelve to fourteen chitinous stomachal plates ; a posterior 

 pallial filament passing through a notch in the shell. Genera Accra, 0. F. 

 Miiller ; British (Fig. 147). Cylindrobulla, Fischer. Volvatella, Pease. 

 FAMILY 7. APLUSTRIDAE, Chenu. Foot very broad ; cephalic shield with 



6' 



Fio. 149. 



Hydatina vexillum, as seen crawling, a', anterior part of the foot ; 6, V, cephalic tentacles ; 

 i, shell. (From Lankester, after Adams.) 



four tentacles ; shell external, thin, without prominent spire. Genera 

 Hydatina, Schumacher (Fig. 149). Aplustrum, Schumacher. Micromelo, 

 Pilsbry. FAMILY 8. PHILINIDAE, Adams. Cephalic shield broad, thick, 

 and simple ; shell wholly internal, thin, the spiral much reduced and the 

 aperture very large. Genera Philine, Ascanius (Fig. 58) ; gizzard with 

 three similar calcareous masticatory plates ; British. Cryptophthalmus, 

 Ehrenberg. Chelinodura, Adams. Phanerophthalmits, Adams. Colpo- 

 daspis, Sars ; British. Colobocephalus, Sars. 

 FAMILY 9. DORIDIIDAE, Fischer. Cephalic 

 shield ending posteriorly in a median point ; 

 mantle well developed ; shell internal, 

 largely membranous ; digestive canal with- 

 out radula and without masticatory plates. 

 Genera Doridium, Meckel. Navarchus, 

 Cooper. FAMILY 10. GASTROPTERIDAE, 

 Fischer. Cephalic shield pointed behind ; 

 shell internal, chiefly membranous with a 

 calcified nucleus, nautiloid ; parapodia well 

 developed, forming fins. Gastropteron, Kosse. 

 FAMILY 11. RUNCIXIDAE, Adams. Cephalic 

 shield continuous with the dorsal integu- 

 ments of the body ; no shell ; ctenidium 

 projecting from the mantle cavity ; four 

 stomachal plates. Genus Runcina, Forbes ; 

 British. FAMILY 12. LOPHOCERCIDAE, 

 Adams. Shell globular or ovoid, external ; 

 foot elongated, the parapodia separate from 

 the ventral surface of the foot ; genital duct diaulic ; visceral commissure 

 short. Genera Lobiger, Krohn ; parapodia divided into two fins on each 



PIG. 150. 



Lophocercus steboldi. A, dorsal 

 aspect ; B, ventral aspect ; C, the 

 shell. /, foot ; /', parapodia or 

 anterior lateral lobe of foot, re- 

 flected on the shell ; TO, mouth ; 

 sh, shell ; t, tentacle. (After 

 Souleyet.) 



