200 CALIFORNIA ACADEMY OF SCIENCES. 



within the body cavity from the base of the penis. Its 

 posterior end is expanded and bifid, the prongs being 

 external and imbedded in the wall of the penis. They 

 extend posteriorly and a little outwards, each being a 

 little longer than half the length of the internal rod. 

 Each prong ends bluntly posteriorly, but some distance 

 in front of its posterior end it gives off a process wide 

 at its base but soon narrowing very much, which runs 

 dorsally a short distance and then turns posteriorly, 

 extending in this direction parallel with the main 

 prong from which it arises past the posterior end of 

 the latter, and then turns inward to meet and fuse with 

 the corresponding process of the other side. This 

 median part is very weakly chitinized. The arc thus 

 formed lies in the dorsal wall of the membranous penis, 

 while the two prongs are lateral. The penis extends 

 some distance beyond all the chitinous parts. The duc- 

 tus ejaculatorius enters it above the internal rod, which 

 latter serves for the attachment of muscles. The intro- 

 mittent organ in this form, then, consists of a membra- 

 nous tube evaginated from the inner end of the genital 

 chamber, in whose walls chitinous rods are developed 

 which unite anteriorly to the ventral wall of the tube 

 and send forward a chitinous rod into the body cavity. 



Colpocephalum osborni. (Plate XIV, fig. 6). 



The genitalia of this species are very similar to those 

 of Trinoton luridum just described. The only difference 

 is that the processes arising from near the posterior 

 ends of the prongs of the fork-shaped structure do not 

 meet each other. In addition to these, however, there 

 is present in the dorsal wall of the membranous penis 

 a chitinous arrowhead-shaped plate, which reaches 

 about half way to the ends of the lateral prongs and is 



