52 



MOLLUSCA. 



na. 



' 



keel, with caudal gland and mucous aperture at end of body. A. cmpiricoruw 

 Fer., Limaac L. Respiratory aperture behind the middle of the right edge of 



the mantle. Sexual opening far removed from respira- 

 " tory aperture behind the right tentacle. Back keeled, 



without caudal gland and mucous orifice. L. agrestis 



L., L. cincreus O. Fr. Mull. 



Fam. Helicidae. Succinea amphibia Drap., Pupa 



muscorum L., Clausilia bldens Drap.. Bulimus monta- 



nus Drap., Helix pomatia L. (Roman snail), H. 



nemoralis L. 



Order 4. OPISTHOBRANCHIATA.* 



Hermaphrodite Gastropods, with flat foot. 

 Branchial veins open into the auricle behind 

 the ventricle. 



The great majority of this order are without 

 a shell. The branchial cavity never contains 



oZo. - JLJons \^co.nfno- * 



lom (Bronn). Br, more than one gill. The gills are usually 

 exposed (fig. 523) or absent. Sometimes there 

 are dorsal processes, into which appendages of the alimentary canal 

 enter (fig. 525). The nervous system contains cerebral, visceral and 

 pedal ganglia (except in Tethys, which has 

 a fused ganglionic mass and simple cesopha- 

 geal commissure). The branchial veins, with 

 a few exceptions (Gastropterori), enter the 

 heart from behind. 



Sub-order 1. Tectibranchiata. Gill al- 

 most always on the right side, covered by 

 the mantle edge or placed in a dorsal 

 branchial cavity. Shell usually present 

 (fig. 524). 



Fam. Pleurobranchidse. With large gill on right 

 side, and usually internal shell. Pleurobranchcea 

 Meckelii Cuv., Pleurobranclius aurantiacm Cuv., 

 Umbrella meditcrranca Lam. 



Fam. Aplysiadae (Sea-hares). Shell covered by 

 two lobes of the foot. Aplysla- depilans L., 

 Mediterranean. 



Fam. Bullidae. Bnlla ampulla L., Phillne 

 aperta L., Acera bullata 0. Fr. Mull. 



FIG. 524.- Pleurolranchus auran- 

 tiacus (regne animal). Sr, 

 gills ; P, penis ; F, tentacle ; 

 B, proboscis. 



Sub-order 2. Nudibranehiata. Marine Gastropods, without shell 



* Alder and Hancock, 1. c. H. Miiller and C. Gegenbaur, " Ueber Phyllirhoe 

 bucephalum." Zeit.f. miss. Zool., Tom IV., 1854. 



