KÜNML. SV. VET. AKADEMIENS HATSfDLtNGAR. HAND 41. K:0 4. 



1 



Opisthobranchia. 



Heart with the auricle mostly behind the ventricle; respiratory organ a ctenidiwm, 

 secondary branchiae or none; nervous system, with a few exceptions, of the euthyneurous 

 type; animal always hermaphrodite. 



Synopsis of Families. 



Subordo I Tectibranchia. 



Right ctenidum usually present, more or less enclosed in a mantle-cavity ; 

 shell mostly present, external or internal, often rudimentary. 



A. Bulloidea (Cephalaspidea) : Head with the tentacles coalesced to a broad disc ; para- 

 podia more or less developed. 



1. Shell external, 



a. with operculum; spire elevated; columella with a strong fold; no para- 

 podial lobes; radula oo.O.oo Fam. Actceonidce.. 



b. without operculum ; spire mostly concealed ; columella with no or only a 

 slight fold. 



+ . Radula absent; no parapodial lobes; in the stomach 3 flat, oval car- 

 tilaginous plates with coarsely tuberculated inner faces; cephalic disc 

 produced in two erected processes behind Fam. Tornatinidoe. 



+ +. Radula present; cephalic disc without produced lobes ; parapodia well 

 developed (except in Diaphana). 



a. Radula narrow, 1.1.1 or (2—5) .1.1.1. (2—5) ; shell compact and 

 inflexible, not covered by the parapodia; stomach-plates 3 calca- 

 reous, or none Fam. Scaphandridoe. 



ß. Radula broad, go . 1 . go ; shell very thin and flexible; aperture 

 with a posterior slit at the suture; parapodial lobes reflexed over 

 the shell ; stomach plates numerous, cartilaginous Fam. Aceridoe. 



2. Shell internal, consisting of two or three whorls only; aperture large; body 

 oblong; parapodial lobes more or less folded over the back; radula without 

 lamina media Fam. Philinidce. 



