XV TECTIBRANCHIATA ASCOGLOSSA 43 1 



Fam. Aplysiidae. — Characters those of the section. Genera : 

 Aplasia (Fig. 287 D), shell arched, flattened, animal large (the 

 "sea hare"); Dolabella, shell sub-triangular (Fig. 286 F) ; Dola- 

 hrifer, shell sub-quadrangular, not spiral ; Notarchus, shell micro- 

 scopic, spiral ; Phyllaplysia, body very depressed, oval, no shell. 



Section III. Pleurobeanchoidea. — Dorsal region protected 

 by a wide notaeum or dorsal covering, or by a shell ; no epipodia, 

 ctenidium large, external, between the right under surface of the 

 notaeum or shell and the foot ; head short, shell present or 

 absent. 



Fam. 1. Fleurohranchidae. — Shell internal or absent, notaeum 

 with spicules, radula multiseriate. Genera : Fleurohranchus 

 (Fig. 286 H), (?) Rcdiotinella, Pleurolranchaea, (?) Neda. 



Faim. 2. Runcinidae. — Branchial lamellae few, under the 

 posterior right notaeum, no shell. Single genus, Runcina. 



Fam. 3. Urifibrellidae.—'^h&\\ external, depressed patelliform, 

 not covering all the animal ; foot very thick, ctenidium large, 

 head depressed, small ; radula multiseriate, teeth innumerable, 

 very small. Genera: Umbrella (Fig. 5a, p. 10), Tylodina. 



Section IV. Siphonarioidea. — Shell patelliform, branchia 

 replaced wholly or in part by a pulmonary sac, pulmonary 

 orifice closed by a small lobe, radula multiseriate, teeth very 

 small. 



Fam. Siphonariidae. — Characters those of the section. Genera : 

 Siphonaria (branchia as well as pulmonary sac), Gadinia (no 

 branchia). These genera, hitherto placed among the Pulmonata, 

 have been recently shown (see p. 19) to be modified Opistho- 

 branchiata. 



Sub-order II. Ascoglossa.-^ — Branchia, mantle cavity, and 

 shell generally wanting, liver ramified, rami enclosed in external 

 papillae (cerata) or beneath the dorsal surface, kidney not com- 

 pact, branched ; radula with one series of strong teeth (Fig. 288), 

 worn out teeth at the front end not dropping off, but preserved 

 in a special sac (acr/co?). 



According to Bergh, the Ascoglossa form a link between the 

 Tectibranchiata, — especially the Aplysiidae and Bullidae — and the 



1 In deference to Bergh 's high authority, the position of a sub-order is here 

 given to the Ascoglossa. It may be doubted whether that position will stand the 

 test of further investigation, and whetlier the families concerned will not be added 

 to the ClMdohcpatic Nudibranchs. 



