Il8 WILLIAM FATTEN. 



said by Woodward to unite the two mandibles does not exist. 

 The plate seen by him was without doubt the displaced thin shelf 

 of bone projecting backwards from the inner surface of the pre- 

 median or ant-orbital, Fig. 2. 



The notched anterior margins of the mandibles are uniformly 

 thin and rounded, and are continuous with the oral membrane, 

 which unites them with the margin of the head, except possibly 

 for a short space near the median line. The lateral margin is 

 narrow and rounded where it becomes continuous with the oral 

 membrane. A broad spur extends laterally on the visceral side 

 of the membrane (Fig. 3) serving no doubt for the attachment of 

 muscles. 



The visceral aspect of the mandibles is nearly smooth, except 

 for what appear to be some indistinct muscle scars and a very 



FIG. 4. A, sagittal section through mandibles and maxillae, a little to one side 

 of the median line of the head ; tnd, mandibles ; mx, maxillae ; r, internal muscu- 

 lar (?) ridge; s.c, sensory canal. J3, transverse section of the mandibles to show 

 heavy median margins. X 



prominent sharp-edged ridge, which extends the whole length of 

 the mandibles, Fig. 4, A, n. 



The maxillae are peculiar S-shaped plates lying behind, or more 

 requently underneath, or dorsal to, the mandibles, Figs. 3 and 5. 

 The median arm of each maxilla usually stands so as to expose a 

 nearly smooth rounded ventral edge and a finely ornamented, some- 

 what triangular, strongly convex posterior surface. The median 

 margin is undulating in outline and with a smooth border. In 



