TECTIBRANCHIATA. 



405 



while most highly specialized in many of its organs, presents the unspecialized 

 features of having an open spermatic groove and a much elongated visceral 

 commissure. 



Section 1. Bulloidea. 



Shell well developed, external or internal (absent only in Runcwia). Head 

 usually without tentacles, with a broad 

 cephalic disc. Epipodia continuous with 

 ventral face of foot. Stomach generally 

 provided with masticatory plates. In Actaeon 

 and the Limacinidae the foot carries a semi- 

 lunar operculum. The pleural ganglia are 

 close to or fused with the cerebral. Visceral 

 commissure long except in the Limacinidae, 

 Cymbuliidae, Cavoliniidae. The visceral com- 

 missure is twisted in Actaeon in the strepto- 



FIG. 317. Actaeon tornatilis (after Pelseneer) x 5. 

 I inferior lobe of mantle ; II pallial gland ; III 

 hypobranchial gland ; I V pallial aperture ; V eye 

 and cephalic shield ; VI penis. 



neurons fashion, and shows indications of the 

 same feature in many other Bulloidea. For 

 instance, in ScapJiander the left half of the 

 commissure passes, ventral to the oesophagus, 

 to the subintestinal ganglion ; while the 

 right half is placed mainly dorsal to the 

 alimentary canal and passes to the supra- 

 intestinal ganglion which supplies the gill 

 and the osphradium. The nerve collar is 

 anterior to the buccal mass in Actaeon, 

 Bulla striata, Philine, Doridium, while in 

 others (Bulla hydatis, B. cornea, Accra, etc.) 

 it is behind. The male and female generative 

 openings may be in common or separate. In 

 the latter case the male opening is at the 

 end of the penis on the right side in front 

 of the mantle opening, while the female is 

 within the mantle cavity (Actaeon}. When 

 there is a common opening (e.g., Cymbuliidae, 

 etc. ) there is a seminal groove to the penis. 



"-XI 



FIG. 318. Nervous system of Actaeon, 

 dorsal view, x 20 (after Pelseneer). 

 I cerebropleural ganglion ; II eye ; 

 III cerebropedal connective, IV 

 nerve from pleuropedal connective, 

 Fpenial nerve ; VI right accessory 

 pallial, VII stomatogastric, VIII 

 supraintestinal, IX sub-intestinal, 

 and XI abdominal ganglion ; X 

 sub-intestinal part of the visceral 

 commissure, XIII supraintestinal 

 part of same ; XII genital nerve ; 

 XI V osphradial and XV left acces- 

 sory pallial ganglion ; X VI para- 

 pedal commissure ; XVII otocyst ; 

 XVIII pedal ganglion ; XIX pleuro- 

 pedal connective. 



Limacinidae, Cavoliniidae, Pelta, 



