MOUTH-PARTS OF THE PAL.EMONID PRAWNS. 



55 



mandible, homologues must be found for the molar process, the 

 incisor process, and the palp. The molar process pretty clearly 

 represents the mandible of the Branchiopoda, and through that 

 the gnathobase of the phyllopod limb. The grinding-surfa.ee of 

 the mandible of Chirocephalus (text-fig. 30) is covered by two 

 comma-shaped patches of fine ridges, each ridge consisting of a 

 row of tubercles, which perhaps represent the rows of stout 

 bristles upon the end of the gnathobases of the trunk-limbs of 

 Notostraca (text-fig. 28). In places the ridges bear some hairs. 

 The commas are reversed, so as to fit against one another, and 

 one patch is narrower then the other and composed of coarser 

 ridges. In view of its structure, position, and function, there 

 can be little doubt that this organ is a specialized gnathobase. 



Text-figure 29. Text-figure 30. 



End view of maxillule of Lepas sp. End view of mandible of Chirocephalus sp. 



Two sets of ridges, very similar to those on the mandible of 

 Chirocephalus, may be recognized at the end of the molar process 

 in Nebalia (text-fig. 31), though here one is of less extent than 

 the other, and seems largely to have been replaced by rows of 

 delicate hairs. Fine ridges, as may be seen in the figures given 

 by various authors, exist also upon the molar processes of various 

 Malacostraca (Anaspides, Gammarus, etc.). In the Decapoda a 

 crescentic or comma-shaped set of serrated ridges is often present 

 (text-figs. 32, 43), with or without patches of hairs and granules, 

 though they tend to disappear, and the molar surface is often 

 broken up into a small number of large lobes. The ridges vary 

 greatly in width, degree of salience, and serration, but are often 



