444 THE AMERICAN NATURALIST. (VoL. XXXIX. 
5. Blood corpuscles pale or colorless. 
Body very slender, usually 10 to 15 mm. in length ; milk-white, creamy, 
or flesh-colored; basis of central stylet very slender; cerebral sense 
organs remarkably large, situated beside brain 
T. albidum Coe, C, S. 
6. With large black or deep brown marking on dorsalsideof head . 7. 
6. Head without conspicuous marking. 
Body 30 to 60 mm. in length ; brownish red above with median white 
stripe; ventral surface white ; without conspicuous lateral grooves on 
e ; * ` ; T. bicolor Coe, A. 
7. Cephalic marking wreath-like. 
Rather slender, 15 to 25 mm. in length ; reddish brown both above and 
below, except head which is white with a sharply marked wreath of 
deep brown color on dorsal surface : ; Zu signifer Coe, S. 
7. Cephalic marking triangular or shield-shaped. 

Fic. 9.— Outline of central stylet and bases. 
A, Tetrast Baer 

B and C, T. nigrifrons. F, T. reticulatum. 
D, T. quadr lineatum. 
Usually 20 to 70 mm. in length ; head provided with two pairs of very 
conspicuous, lateral, oblique furrows. Color very variable, except head 
which is white with shield-shaped or triangular marking of deep brown 
color on dorsal surface. Body deep purple, deep brown with white 
dorsal longitudinal band, reddish with brown flecks, pale brownish, or 
on dorsal surface ; of similar color, but paler, and often with white 
longitudinal band, on ventral surface : . I. nigrifrons Coe, C. 
8. Flesh-color or yellowish, mottled, especially on dorsal surface, with brown- 
ish blotches and dots of various shades, often mainly collected into a 
series of transverse bands ; body slender, 8 to 15 mm. in length 
T. (Gzrstedia) dorsale (Abildgaard) McIntosh, C, X, Y. 
