450 CALIFORNIA ACADEMY OF SCIENCES. 



the ventral side. Posteriorly there is a thick, rounded, 

 median process which projects backward from near the 

 dorsal edge of the sclerite, but still some distance below 

 it, so that it is free from and not imbedded within the 

 wall of the pharynx. 



The sclerite, viewed ventrally, is somewhat shield- 

 shaped in profile. The body is almost semicircular, with 

 a small segment taken off in front bv the anterior trunca- 

 tion referred to. Posteriorly there projects the median 

 rounded process, and anteriorly on each side the anterior 

 lateral processes. The latter give to the anterior profile 

 an emarginated appearance. In the middle there is a 

 longitudinal light colored area, due to the cavity on the 

 dorsal side, the floor of which, being thinner than the 

 other parts, transmits more light in mounted specimens. 

 This area is expanded near the front, contracted from 

 side to side posteriorly, and rounded before and behind. 

 Along the median line there is a narrow linear area still 

 lighter in color, due to a groove in the bottom of the dor- 

 sal hollow. 



The dorsal surface of the sclerite is, as already de- 

 scribed, excavated, and is doubly so, there being one 

 cavity situated within another. The upper of these is a 

 shallow depression, having its edges rather oval in out- 

 line. In front it extends very near the anterior borders 

 of the sclerite, but on the sides the edges of the cavity 

 and those of the sclerite are considerably separated; and 

 that portion of the dorsal surface between these two is 

 rounded outwardly and ventrally. This space is nar- 

 rowed again posteriorly, but not so much as in front. 

 The inner cavity is situated in the floor of the other. It 

 is much deeper, and its walls are steep, meeting the in- 

 terrupted walls of the other at a considerable angle. It 

 is this deeper cavity that forms the light colored area 



