OF WASHINGTON. 273 



illustration it becomes clear that the author has observed the 

 large stigmal plate, which every mature Tick possesses. Mr. 

 Murray, of England, the author of a series of -hand-books on nat 

 ural .history, discovered among the collection in the South Ken 

 sington Museum a genus which he named Xyphiastor, and bases 

 the criterium on the following characteristics : "Flat, mouth pro 

 vided with a long, projecting rostrum and long palpi applied to it, 

 abdomen with posterior margin beaded." The same author bases 

 a new genus solely on the fact that its members live or have been 

 found on serpents. 



After these few preliminary remarks on the present state of our 

 knowledge of this interesting group, I proceed now to the subject 

 of my address. 



In the Cynorhcestea, as in other suborders and families of the 

 great order Acari, the cephalothorax is coalesced with the abdo 

 men into one solitary body, and the traces which seem .to indicate 

 the original divisions are so obscure that it is difficult to decide 

 whether, in following them, we explain correctly the true organ 

 ization. These traces are, First, a shield on the dorsal surface, 

 which in the Antistomata is present in both of the immature 

 stages of the two sexes and also in the fully developed female, 

 while it is absent in the mature male. This shield occupies in 

 the young larva, and in the nymph in the free state, nearly one- 

 half of the abdominal region, and as it does not grow with the 

 rest of the body it is in the full-fed stage of the nymph, and es 

 pecially in the full grown female, of comparatively small size. 

 That it is rather a cephalic than a thoracic shield, as Packard 

 states, I infer from the fact that it bears on its sides the eyes, if 

 such be present. 



Second, The orifice of the oviduct in the mature female and 

 that of the sexual organs of the male are situated very close to the 

 insertion of the capitulum, and, as these organs are always placed 

 on the abdomen, I infer that the abdomen reaches close to the 

 anterior border of the body. If this be true, the distinct and im 

 pressed line which runs in both sexes in front of these orifices, 

 and backward and outward on both sides, would be the trace of 

 the border between the cephalothorax and the abdomen. In 

 other words, the abdomen would be wedged into the mid 

 dle region of the cephalothorax, and this part would surround 



