198 CALIFORNIA ACADEMY OF SCIENCES. 



turned inward — relatively opposite to that of the left 

 prong. 



The bifid posterior end of the internal plate is 

 imbedded in the base of the chitinous penis. The outer 

 prongs are attached to the arms of the bifurcation in a 

 manner much different from that in other forms. The 

 base of each prong is a little expanded and bears two 

 tapering processes projecting inwardly and anteriorly, 

 one lying dorsal to the other. The dorsal process is the 

 larger; it is curved so that the posterior margin is con- 

 cave and the anterior convex. The tips of the dorsal 

 processes of the two sides are directed toward and lie 

 close to each other. Each is connected by a delicate 

 dorsoventrally flattened chitinous bar, which passes 

 outward to the arm on the same side of the bifid base 

 of the internal plate, and fuses with it very near its 

 posterior ends. The ventral process is smaller than 

 the dorsal one; its posterior edge is convex and its 

 anterior edge concave. The end of each arm of the 

 plate abuts upon the corresponding prong between the 

 bases of the two processes of the latter, the transverse 

 slender bar of chitin serving to connect the two other- 

 wise separated parts. Lying in the dorsal wall of the 

 membranous penis is a thin chitinous plate. It ex- 

 tends from near the bases of the lateral prongs to a 

 short distance from the distal end of the smaller one. 

 It also is symmetrical. The right edge is about straight 

 and distinctly marked; it lies nearer the side of the 

 penis than does the left edge, so that the plate is not 

 median. The left edge is much less sharply defined 

 and extends obliquely from the left side of the base of 

 the penis posteriorly and toward the middle line. To 

 the dorsal side of the internal plate is attached a large 

 mass of muscle fibers, and on the same side of the 

 plate the ductus ejaculatorius enters the penis. 



