RUNCINA. 171 



situated further forward, on right side of cephalic region. Stomach 

 armed with four denticulate plates. 



Radula with the formula 1.1.1 (pi. 68, f. 36). Jaws present. 



A very distinct family of minute limacoid Tectibranchs, resem- 

 bling Pleurobranchidce somewhat in outward aspect, but differing 

 widely in the dentition, the stomach- armature and the absence of 

 rhinophores. Pelseneer believes Rundnidce, to belong to the Cephala- 

 spidea (Chall. Rep. Zool. pt. Ixvi, p. 97); I think this likely. 



The original discoverer of the European species, Quatrefages, 

 placed it in his supposed degenerate group " Phlebenterata," charac- 

 terized by lack of a circulating system, anus, etc. Forbes, who re- 

 discovered it on the English coast, placed the group next to Lima- 

 pontia, an arrangement in which some other authors concurred. 

 Gray, however, in 1857, decided its affinities to be with Pleuro- 

 branchidce, Umbrellidce and Tylodinidce, a position retained by 

 Vayssiere. The important work on the group by the latter author, 

 together with that of Bergh on the genus Ildica, supplies all that is 

 yet known of the internal anatomy of Rundnidce. 



Synopsis of Genera. 

 Genus RUNCINA Forbes. 



Tentacles or rhinophores none. Teeth of the radula denticulate. 

 Shell reduced to a minute vestige buried in the posterior part of the 

 integument. 



Genus ILDICA Bergh. 



Small labial tentacles developed. Teeth not denticulate. Shell 

 a small non-spiral calcareous plate, external and posterior on the 

 back. 



Genus RUNCINA Forbes, 1853. 



Rundna FORBES, Hist. Brit. Moll, iii, p. 611, type R. hancocki. 

 Pelta QUATREFAGES, Ann. Sci. Nat. (3), i, p. 151 (1844), type P. 

 coronata. VAYSSIERE, Ann. Sci. Nat. (6), xv, p. 6 (1883). Not 

 Pelta Beck, Index Moll., p. 100 (1837). 



Shell membranous, internal and minute. Body lengthened, lima- 

 ciform ; no tentacles at sides of mouth. Teeth of radula denticulate. 

 Type R. coronata. 



