8 IXODOIDEA, OR TICKS, OF THE UNITED STATES. 



and broad, and the apical is very small and often situated in a 

 depression near the tip of the third. The palpi are usually some- 

 what concave on the side toward the mouth parts, so that they may 

 sheath these parts. The comparative lengths of the second and third 

 joints of the palpi give useful characters in separating the genera of 

 ticks. 



On the dorsum of the capitulum of adult female ticks there are 

 two depressed pitted areas known as the porose areas. No one has 

 as yet determined their function. All female ticks of the subfamily 

 Ixodina? which do not have these organs fully exposed are imma- 

 ture and should not be described as new species. Various species, 

 and even genera, have been based on immature forms, owing to a 

 failure to recognize this point. The genera Phaulixodes.^ Herpetohia^ 

 Sarconyssus, and Gonixodes fall in this class. 



The shield is usually irregularly hexagonal in shape. On each 

 lateral margin is a pale eye-like spot or ocellus ; in some genera these 

 eyes are wanting. The posterior margin of the body in most forms 

 is marked by a number (8 to 10) of short impressed furrows, which 

 outline a series of lobes or festoons; these are more distinct in the male 

 than in the female, and when the latter is distended with blood they 

 are barely visible. On the underside or center of the body there are 

 two median apertures; the anterior one not far from the beak is the 

 genital pore; the posterior one is the anus. In mau}^ forms there is a 

 curved groove behind the anus and from it a median furrow, while 

 in other species there is a curved groove in front of the anus and 

 reaching back each side toward the margin of the body. In all forms 

 there is a more lateral groove each side reaching forward to the geni- 

 tal pore. In the males of several genera there are one or two cor- 

 neous triangular plates each side of the anus, the anal plates. Occa- 

 sionally the abdomen terminates in a median process, or tail. 



The legs arise from each side of the anterior part of the venter; 

 the coxa3 are sometimes close together, sometimes more widely sepa- 

 rate. The legs are usually slender, subequal in length, but the fourth 

 pair is rather the longest, and sometimes larger than the others. 

 Each is composed of at least six joints, as follows, from base outward : 

 Coxa., trochanter., femur., tibia, metatarsus, and tarsus. The latter 

 is commonly more or less definitely divided into two parts. At the 

 tip of the tarsus is a pair of large claws situated on a rather long- 

 pedicel, and between them is usually a pulvilhim. On the upper sur- 

 face of tarsus I is a pit covered by a membrane; this is known as 

 Ilaller''s organ., from its discoverer, and is supposed to be an organ of 

 audition. One or more of the coxfie are armed behind by spine-like 

 processes or teeth. In the males of some species the hind coxa? are 

 greatly enlarged. Above, and usually slightly behind the hind coxae, 

 are the stigmal plates containing near their centers the stigmal orif.ce 



