THE LAMELL1BRANCHIA 



219 



palps, but usually the palps become suddenly much broader than 

 the lips. The palps are formed from part of the velar area of the 

 larva and assume various forms, but are most commonly triangular. 

 Their inner surfaces are transversely folded arid ciliated in such a 

 manner as to conduct all particles coming within their reach into 

 the buccal orifice. They are poorly developed or absent in various 

 Lucinidae, such as Axinus (Fig. 238) and Corbis, and in Limopsis and 

 some species of Cuspidaria. On the other hand, they are very large 

 in the Tellinidae, surpassing the gills in size in this family, and the 

 anterior pair is very large in Poromya (Fig. 249, a.p). In the 



st 



Fio. 200. 



An adult specimen of Yoldia livwtula, as it appears while feeding partially immerged in 

 mud. e.s, exhalant siphon ; i.s, inhalant siphon ; p.ap, palp appendages ; s.t, siphonal tentacle. 

 (After Drew.) 



Nuculidae and Ledidae the posterior angles of each pair of palps 

 are produced to form a common tentaculiform appendage bearing a 

 groove along the whole of its ventral surface ; these appendages can 

 be thrust out beyond the shell and assist in obtaining food (Fig. 

 200, p.ap). In Solenomya the two palps are rudimentary, but the 

 tentacular prolongation persists in the form common to the other 

 Protobranchia, with its ventral groove forming a continuation of the 

 interlabial space (Fig. 231, p.l.). 



In the family Nuculidae among the Protobranchia there is still 

 an anterior dilatation of the alimentary canal representing the buccal 

 cavity and provided with two lateral and symmetrical glandular 



