THE LAMELLIBRANCHIA 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 and 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 Avxinus (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 
Fie. 200. 
An adult specimen of Yoldia limatula, as it appears while feeding—partially immerged in 
mud. e.s, exhalant siphon ; 7.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./.). 
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 
