444 CALIFORNIA ACADEMY OF SCIENCES. 



is a condyle which articulates with a facet on the dorsal 

 side of the mandible. This facet is more external than 

 the condyle of the mandible, and is also farther forward. 

 In all these points the mandible is extremely similar to the 

 corresponding one of Ancistrona. The retractor muscle 

 is attached directly near the inner posterior angle. 



The left mandible is in general similar to the right, and 

 agrees with the corresponding mandible of Ancistrona in 

 the same way as the right one does, although the two are 

 rather less alike than those of Ancistrona gigas. 



The posterior tooth of the left mandible is continuous 

 from the dorsal surface, but is very small compared with 

 the anterior one, and is sharp-pointed compared with the 

 corresponding tooth on the right side. The anterior tooth 

 is much the same as that on the right side, or is perhaps 

 a little smaller. Back of it is a depression on the inner 

 part of the ventral surface; this is bounded behind by an 

 elevation which is continuous inwardly as a slender pro- 

 jection from the ventral surface, just as in the case of 

 Ancistrona gigas. This process is thick at its base but 

 tapers distally to the rounded termination. Its anterior 

 border is convex, but on the distal half of the posterior 

 margin is a rather deep, rounded concavity. To the outer 

 angle of the base is attached the extensor muscle. This 

 is rather large on each side of the head. Internal to the 

 attachment of the extensor muscle is the articulating- con- 

 dyle, and dorsal to the latter the rather large facet. 

 These articulate as on the other side, with a facet and 

 condyle, respectively, of the ventral aspect of the 

 head. 



