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BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



backward toward the median line, but fades out gradually before 

 meeting its fellow; on the ventral side the furrows extend obliquely 

 forward and join in the median line not far behind the rhyncho- 

 daeum opening (PL 18, fig. 112). The jDosterior furrows are much 

 more conspicuous, often forming a distinct fluted collar (PI. 18, fig. 



111). 



Color. — Variations in color and markings so striking that several 



species would appear to be represented by individuals which actually 

 present all degrees of intergradation. All color varieties agree in 

 internal organization, and also are similar in having a whitish or pale 

 yellowish head provided with a dark dorsal marking of variable 

 size and shape (PI. 2, fig. 26; PI. 18, figs. Ill, 113); ventral side of 

 head whitish or very pale gray in all varieties. Blood corpuscles 

 deep red in color. The three more distinct color varieties are as 

 follows : — 



Variety purpureum (PI. 2, fig. 26). Head opaque white, with 

 large, shield-like dark brown dorsal marking, rounded in front and 

 deeply bilobed in median line ; white coloi- of head extends a short 

 distance back of marking, or as far as the posterior oblique furrows, 

 where it abruptly changes to a deep, rich purple, which color 

 extends to posterior end of body. Ventral surface of same general 

 color as the back, but somewhat paler and with a more reddish 

 tinge ; often with a much paler median band anteriorly. Ventral 

 side of head whitish, separated abruptly fi'om purple color of body. 

 Variety bicolor. Head whitish with tinge of brown, with bi-oad, 

 triangular dark brown dorsal marking which is widest behind, with 



its obtuse apex in the median line anteri- 

 orly. C^olor of body deep brown with a 

 narrow median band of white. Brown 

 color is darkest along the borders of the 

 median white band, and is much ])aler 

 laterally ; toward the lateral margins of 

 body it becomes pale brownish, and this 

 color continues to the ventral surface, be- 

 coming gradually paler toward the median 

 line. 



The third variety, joai/iW;//??-, is much 

 less deeply colored than those above de- 

 scribed, and deep brown marking on the head is much narrower, 



Fig. 57. — Tetrastemma nigri- 

 frons. Stylet apparatus of 

 proboscis 



