408 



MOLLUSCA. 



tentacles, the posterior pair with eyes. The median part of the foot consists 

 of a posterior lobe and two antero-lateral lobes joined in front (horse-shoe- 

 shaped) ; the epipodia or fins are quite separate from this median part of the 

 foot and from the head. The penis is latero-ventral on the right side of 

 the foot ; a groove leads to it from the genital opening. There is an evaginable 

 proboscis generally bearing suckers or appendages with suckers. These have 

 nothing to do with the foot. The buccal cavity contains evaginable hook-sacs 

 opening on each side of the radula. The jaws are united ventrally in the middle 

 line. The stomach is without plates. The anus is on the right side. The 

 cerebral ganglia are closely approximated on the dorsal side of the oesophagus, 

 and the pleural are near the pedal ; iy. this they differ from the so-called 

 thecosomatous Pteropods, and resemble the Aplysiidae, There may be 

 branchial processes of the integument a lateral one on the right side and 

 a posterior gill. 



Te 



Fl 



FIG. 321. a, Pneumoderma violaceum (from Bronn) from 

 the ventral surface, b, Clione australis (regne animal) 

 from the side. Fl fins (epipodia); Te appendages of 

 the proboscis, with suckers in o. 



FIG. 322 Larva of Pneumoderma 

 (after Gegenbaur). 



Fam. 2. Pneumodermatidae. With suckers on the proboscis. Dexiobranchaea 

 Boas ; Pneumoderma Cuvier (Fig. 321) ; Spongiobranchaea d'Orb. 



Fam. 3. Clionopsidae. Without suckers and buccal appendages. Proboscis 

 very long. Posterior gill tetraradiate. Clionopsis Troschel. 



Fam. 4. Clionidae. With conical glandular buccal appendages (cephalocones). 

 No gill. Clione Pallas (Fig. 321). 



Fam. 5. Notobranchaeidae. With conical buccal appendages, without 

 lateral gill. Notobranchaea Pelseneer. 



Fam. 6. Halopsychidae. Body ovate, rounded behind ; without gills or 

 proboscis ; fins broadened at the ends. Halopsyche Bronn. 



Section 3. Pleurobranchioidea. 



The head has two pairs of tentacles, of which the posterior are the rhino- 

 phores ; the foot is without epipodia ; the mantle-cavity is shallow and contains 

 a large ctenidium on the right side. The male and female generative openings 

 are near but separate, and there is no seminal groove. The pleural ganglia are 



