CASTLE : NORTH AMERICAN RHYNCHOBDELLID^. 55 



in Figure 6, Plate 2. They include five longitudLual rows of papillae found ou 

 the middle (sensory) annuli of usually all the triannulate somites. These rows 

 may be designated, from their position, median, marginal, and intermediate, the 

 first named being unpaired, the other two paired. 



A row of papillae is found also between the median and each intermediate 

 row, but these papillae are situated not on the middle, but on the posterior 

 annulus of each of the somites from about viii. to xxii. inclusive (Figure 6). 

 These will be designated paramedian rows. 



The most conspicuous papillae of somites xsv.-xxvii. are usually placed as 

 indicated in Figure 6. They consist, first, of a continuation of the marginal 

 rows back to the anus; secondly, of two rows of three papillae each, placed one 

 on either side of the median plane and too near it to fall in the paramedian 

 rows found f;irther forward. 



Other less conspicuous papillfe occur on the dorsal surface of the body and 

 posterior sucker, but no papillae are found on the ventral surface of the 

 animal. 



The general color of the body above is brown variegated with yellow, orange, 

 and green. Light areas of yellow or pale orange form : — 



T. A median vitta extending from the anterior end of the body back to somite 

 XXV., usually without interruption, but not always so, and expanding commonly 

 at six places, namely, (1) in somites vi. and vii. (Figure 32, Plate 8) ; (2) in 

 somite ix. ; (3) in somites xii. and xiii. ; (4) in somites xv. and xvi. ; and 

 (6) in somite xxii. (and the posterior part of somite xxi.). The median row 

 of papUlse already described falls entirely in the median light vitta. In somites 

 XXV. -XXVII. both vitta and papillae become double, dark pigment being found 

 along the median line back to the anus, usually behind it also quite to the 

 posterior margin of the acetabulum. The double (or paramedian) light vitta 

 of somites xxv.-xxvn. contains the three pairs of papillae sho'ftTi in Figure 6, 

 Plate 2 ; it may or may not be continuous with the median light vitta farther 

 forward. 



II. Throughout the greater part of the body the papillae of the intermediate 

 rows lie each in an irregularly rounded light spot. The successive spots of 

 each half of the body may become confluent so as to form an irregular, 

 frequently interrupted, longitudinal band. 



III. The margins of the body are conspicuously marked with metameric 

 light spots from about the third or fourth somite back to somite xxv. Some 

 idea of the form and position of these spots may be obtained from an examina- 

 tion of the stippled areas in Figure 6, Plate 2, and Figure 32, Plate 8. Each 

 spot is t)"pically V- or U-shaped and is placed on the adjacent non-sensory rings 

 of two successive somites. The usually hollow centre of the V or U is formed 

 by a spot of brown sometimes bordered with orange. The margin of the sen- 

 sory ring is generally darker in color than its more median parts, so that it is 

 strongly in contrast with the metameric light spots which it separates. 



The posterior sucker is decorated with radially placed triangular light spots 

 (Figure 6) resembling the marginal spots of the body. Other irregularly 



