42 RUNCINIDiE. 



Genus TYLODINA, Rafinesque. 



Tentacles dorsal, ear-like, with the eyes sessile at their 

 outer bases; labial appendages lanceolate, united by a veil, 

 emarginate in front. Foot strong, thick, ovate, truncate in 

 front. 



Shell external, membranous, oval, conical, with a callous, 

 sub-central, recurved apex of about two whorls. 



Ex. T. punctulata, Rajinesque, pi. 01, fig. 4. Shell, T. 

 punctulata, fig. 4, a. 



Tylodina differs from Operculatum in the head being- 

 produced and bifid, and in the membranous structure of 

 the shell. Of this genus there are three species already 

 described, two of which are inhabitants of the Mediter- 

 ranean, and one is a native of the coast of Norway. 



Species of Tylodina. 



citrina, Joannis. punctulata, Fiqfin. 



Duebenii, Loven. 



Fam. RUNCINIM1. 



Tongue-membrane armed with three series of teeth, the 

 central broad, transverse, with the upper edge reflexed, 

 notched in the middle, and denticulate on each side ; the 

 lateral large, versatile, conic, arched, compressed, with an 

 acute tip. Cephalic disk flat, broad, and sub-quadraugular; 

 the eyes sessile on its upper surface. Mantle distinct, 

 oblong ; gills slightly pinnate, at the hinder part under the 

 edge of the mantle on the right side. Vent central, on the 



