S. I. Smith — Eavh/ St<iges of Hippa talpoida. 339 



very long, plumose seta? extending along each side of the lal)runi. 

 At the sides of the oral opening are the mandibles (c, d, e), the tips 

 of their paljti (g) approachhig each other just in front of it. The 

 mesial side of the basal portion of the mandible is consolidated with 

 and forms a part of the raised lateral margin of the oral opening, 

 while the outer side is continuous with and consolidated to the buccal 

 walls each side. The palpus arises from this basal portion of the 

 mandible and inwraps the posterior part of the margin of the labrum 

 by means of an oblique fold, which distinctly separates it into an 

 outer ((/) and an inner {e) portion. This oblique fold is most marked 

 at the anterior extremity of the palpus, where it presents a sigmoid 

 curve, the thickening of the palpus posteriorly rendering it less 

 distinct though well seen in a transverse section, as in figure 10a. 

 The free margin {d, figure 10) of this outer portion is thickly armed 

 with a series of stout spinules, while the inner portion projects above 

 the posterior part of the labrum, as a broad, oval-pointed, lamelliform 

 lobe, the edges of which are thickly beset with slender seta?. The 

 coronal portion (c) of each mandible is a broad, obtusely rounded, 

 thin lamella, the free terminal part of which lies just above the 

 palpus. Each lamella of the deeply bifid labium ( /') lies just above 

 the mandible each side and closely infolds the margin of the oral 

 opening. 



The protognathal portion of the first maxilla (Plate XLVII, fig. 8) 

 is divided into two deeply separated lobes and fits closely upon the 

 labium and mandible. The somewhat oval, terminal portion of the 

 posterior, or inner, lobe («, fig. 8) lies just over the lobes of the 

 labium each side, and the whole length of its nearly straight, inner 

 margin is lient downward into the posterior part of the oral opening, 

 and is edged with a double series of long, serrate setjie ; while the 

 outer convex surface is armed with a scattered, double line of minute 

 spinules. This terminal poition of the lobe is free all round, except 

 near the outer, posterior angle wdiere it is connected with the buccal 

 walls, and where a thickened, rod-like portion connects it, by an 

 imperfect articulation, w^ith the l)ase of the anterior lobe. The anterior 

 lobe (h) is very long and narrow, and its oblique, terminal margin 

 lies just over the inner portion of the mandibular ])alpus, and is 

 thickly armed with short, setiforni spinules, while the lateral margins 

 are thickly clotlied with slender, ])limiose seta^, of which those at the 

 anterior extremity of the outer margin are very nuich the longest. 

 The palpus (c) is soft and sack-like, arises from near the base of the 

 anterior lobe, and projects laterally into the etterent passages of the 

 branchial chamber. 



