Prof. H. Karsten on Rhynchoprion penetrans. 301 



maxillse have not again been detected, although, they are pre- 

 sent, and nearly of the form figured by Duges. These maxilla? 

 (PI. IX. figs. 3, 4, & 13) are so broad that they cover the base 

 of the mandibles with their anterior margins, which do not pro- 

 ject beyond the cheeks, but are fringed with several rows of 

 fine seta? directed downwards. They are flat, almost triangular, 

 lie close together, and bear on their outer surface, near the upper 

 margin, the four -jointed palpi (PI. VIII. figs. 3 & 8, and PI. 

 IX. figs. 1 & 13), which are roughly setose above, and of 

 which the lowest, longest joint is bent inwards at its base, and 

 furnished on the outer surface of the curvature with a circular 

 orifice, or, rather, membranaceous spot. 



The length of the first three joints of these palpi varies remark- 

 ably in different individuals : sometimes these are all of equal 

 length ; sometimes the third is the largest ; sometimes the second 

 exceeds the other two. The comparative length of these joints 

 furnishes no certain and constant character. 



The mandibles (PL IX. figs. 12 & 13) are about one-fourth 

 longer than these maxillary palpi, and remarkably similar both 

 in form and size to those of Pulex irritans, Linn. : their form is 

 that of linear, shallow channels ; on the margin and external sur- 

 faces along the margin they are nodosely notched and striated ; 

 in the median line of the organ these stria? are separated from 

 each other by a smooth surface. At the base, which is covered 

 by the maxilla?, the striation is lost at the upper margin, and is 

 only indicated by some acute denticles standing singly on the 

 margin. At the apex itself (PI. IX. fig. 12), where the nodose 

 stria? of the lateral surfaces are much diminished, and only in- 

 dicated by a few knots, there is, in each mandible, at the extre- 

 mity of the smooth median surface, a small hook, curved out- 

 wards and attached by an enlarged base, which is no doubt 

 partly the cause of the difficulty of extracting the animal when 

 still capable of quick motion and engaged in boring into the 

 skin. 



In the cavity of parabolic section which these two channeled 

 bodies enclose between them is situated the median piercing- 

 organ (PI. IX. figs. 13 & 14), the analogue of the epipharynx 

 of the Diptera, the much-dilated base of which lies under the 

 vertex, above the eyes, and forms the commencement of the 

 oesophagus. This organ also is a channeled body, the hollow 

 side of which is turned downwards (figs. 10 & 11). Although 

 at the first glance this organ resembles a two-edged linear 

 lamina, it is nevertheless prismatic in form, as its lateral walls 

 diverge more or less rectangularly. The dorsal surface forms a 

 sharply projecting cutting-edge, furnished at the anterior extre- 

 mity with three distant teeth, of which the last one, nearest the 



