448 CALIFORNIA ACADEMY OF SCIENCES. 



until the anterior margin becomes the ventral margin. All 

 the apparent differences may be reconciled by this view. 

 In accordance with it the articulating surfaces lie as they 

 should. Further, the mandibles being as in the other 

 genera, two-toothed, the posterior rounded tooth of An- 

 cistrona, arising from the inner dorsal margin, lies in this 

 form on the anterior inner aspect, in front of, and dorsal 

 to the larger tooth. 



The left mandible has also the long slender process at 

 the inner part of the base, as in Ancisirona and Lcemo- 

 bothrium ; but, as would be expected, this arises from the 

 dorsal aspect of the base. Since, however, in Euryme- 

 topits it is very long and slender, it is bent backwards so 

 as to lie parallel with the head. In Goniodes cervinicornis, 

 however, it is shorter and projects inwardly. 



The mandibles of jEurymetofius taurus are entirely ex- 

 posed on the ventral surface of the head, not even their 

 bases being covered by the labium. They are thick and 

 have a clumsy appearance. The anterior articulating 

 surface is a large facet situated at the anterior outer angle 

 of the mandibles, on the dorsal surface. A rounded pro- 

 cess projects over it from below. The posterior outer 

 part of the mandible, bearing the condyle by which it is 

 articulated posteriorly, is greatly prolonged backward, 

 forming a long process bearing the condyle at the ex- 

 tremity. The latter fits into a chitinous socket on the 

 ventral surface of the head. Some distance in front of 

 this is a condyle which fits into the facet of the mandible. 

 The process above referred to, arising from the inner 

 dorsal aspect of the left mandible, curves inwardly and 

 posteriorly. It is very wide at its base but rapidly dimin- 

 ishes distally, and ends by a slightly enlarged extremity, 

 free in the mouth cavity. The ventral tooth of each man- 

 dible is large and thick, and bluntly pointed. The dorsal 



