Prof. H. Karsten on Rhynchoprion penetrans. 303 



sent any sexual variations, with the exception of diiFerences in the 

 form of the external generative organs. The feet (which were 

 correctly described by Duges) and the head and thorax are very 

 similar in form in the two sexes. 



The head is somewhat flattened on the vertex, which borders 

 the perpendicular, almost triangular forehead, and is separated 

 from the forehead and cheeks by a somewhat prominent ridge, 

 having a row of small, straight, strong bristles. The occiput, 

 which is arched and covered with very delicate hairs, comes 

 down upon the flat, nearly concave, and likewise finely haired 

 vertex in the form of a median ridge, which is completely obli- 

 terated at the frontal margin. 



The large oval eyes are simple in both sexes, the cornea 

 covering them exhibiting no facets. The very large optic nerves, 

 which, like cerebral hemispheres, occupy a great part of the 

 head, nevertheless show very distinctly on their surface the ends 

 of the numerous nervous filaments of which they are composed. 



Behind the eyes, sunk in a pit of the cheeks, are the large 

 three-jointed antennae, the oval terminal joint of which is covered 

 with fine setae, and appears to be pierced on the upper and pos- 

 terior side by a row of six oval attenuated spots, each of which 

 is circumscribed by a thick ring. At its obtuse end this oval 

 organ is attached by means of a long cylindrical stalk to the 

 middle joint, which is of nearly the same size and of a clubbed 

 hammer-shape ; and this stalk is inserted in a circular orifice in 

 the latter, within which it can be retracted. The delicate mem- 

 branes above mentioned as closing the apparent orifices in the 

 free oval terminal joint are protected from contact from without 

 by means of long setse curving over them, which spring from 

 the hammer-like projection of the middle joint near the orifice 

 already described. The very small ellipsoidal basal joint is in- 

 serted at one end into the upper posterior angle of the anten- 

 nary pit, and at the other simply articulated to the second joint 

 (PL VIII. fig. 2). 



The three narrow but free thoracic segments, of which the 

 posterior is partially concealed by the hinder margin of the pre- 

 ceding one, are somewhat dilated below, where they are pierced 

 by a stigma which leads into a narrow trachea ; with their low- 

 est extremities they border the three immoveable epimera into 

 which the coxse are articulated. 



The third or hindmost of these coxse terminates below and 

 anteriorly in the large and striking spinous process, to the dis- 

 covery of which Guerin attributed great importance. The very 

 powerful femur, which is united to this large posterior coxa 

 by means of the trochanter, bears a series of strong bristles 

 along the middle line of its outer surface. The fi*'«.t tarsal joint 



