52 



MOLLUSCA. 



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

 Fer., Umax 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. ugrestis 

 L., L. cinerevs 0. Fr. Mull. 



Fam. Helicidae. Sued/tea amphibia Drap., Pupa 

 mi/xcorum L., Clavxiliu bidens Drap., Sulimus monta- 

 nvs Drap., Helix pomatia L. (Roman snail), If. 

 nemoralis L. 



FIR. 



Order 4. OPISTHOBRANCHIATA.* 



Hermaphrodite Gastropods, with fiat 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 



523. Dons (AcantJio- 



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

 gins; 4, anus; F, tentacle. expoged ( fig 533) 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 oesopha- 



geal commissure). The branchial veins, with 



a few exceptions (Gastropteron), 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). 



Fain. Pleurobranchidse. With large gill on right 

 side, and usually internal shell. Pleurobranchaa 

 Jfcrftelii Cuv., Ph'iirobrancltus aurantiacus Cuv., 

 Umbrella medlterranea Lam. 



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

 two lobes of the foot. Aplysia depilans L., 

 Mediterranean. 



Farn. Bullidae. Bulla ampulla L., Philine 

 apcrta L., Acer a bullata 0. Fr. Miill. 



Br 



FIG. 524.- Pleurobranchjts nnran- 

 tiacux (regne animal). Br, 

 gOls ; P, penis ; F, tentacle ; 

 R, proboscis. 



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



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

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



