IO COE 



ORDER HETERONEMERTEA. 



A. Head without deep lateral, longitudinal furrows. Proboscis mus- 

 culature of two layers Tceniosoma, p. 6 1 . 



i. Of very large size, reaching a length of 2 meters and a diameter of 18 mm. 

 Deep yellow, thickly sprinkled with small irregular, dark red spots. 



T. princeps, p. 62. 



AA. Head with deep, horizontal furrows. Proboscis usually with 



three muscular layers and muscular crossings. 



a. Caudal cirrus absent. Body long and slender, rounded or flat- 

 tened; very contractile Lineus, p. 64. 



1. A single row of 4-6 (or sometimes 8) ocelli on each side of head. Dusky, 



or brownish green, dark brown, or reddish brown ; commonly paler 

 beneath L. viridis, p. 65. 



2. No ocelli in adult. Dark, reddish brown or purple, with a narrow trans- 



verse white band connecting posterior ends of cephalic furrows across 

 dorsal surface of neck L. torquatus, p. 66. 



aa. Caudal cirrus present. Body rather firm ; incapable of swim- 

 ming Micrura , p. 68. 



1. Dorsal surface deep purple or wine-color with 15-40 sharp, pure white, 



transverse lines ; tip of snout with triangular, bright orange spot ; 

 ventral surface of body pure white M. verrilli, p. 68. 



2. Body flattened, grayish brown above with narrow, colorless, transverse 



lines ; with a small, flesh-colored, sub-truncate head, much narrower 

 than body, and with minute gray spots near antero-lateral margins. 



M. impress a, 1 p. 70. 



3. Salmon or flesh-color (more rarely light brownish); lighter, with tinges 



of brighter red, or nearly colorless anteriorly. Intestinal lobes more 

 deeply colored, sometimes chestnut-brown. A cream-colored stripe is 

 conspicuous in the ventral median line M. alaskensis, p. 71. 



aaa. Caudal cirrus present in perfect specimens, but often missing. 

 Body long and flat, with thin lateral margins. Swims read- 

 ily. Dorso-ventral and diagonal muscles well developed. 

 Eyes usually absent Ccrebratulus, p. 74. 



1. Very large and stout, becoming 2 meters or more in length, and 25 mm. 



in width. Dark, reddish brown C. herculeus, p. 75. 



2. Large and ribbon-like. Slaty brown to grayish green, with thin, white, 



lateral margins C. marginatus, p. 75. 



3. Rather short. Chestnut-brown or reddish brown in esophagal region, 



chocolate-brown in intestinal region above; brownish flesh-color to 

 dark brown beneath, with a median longitudinal ochre stripe along 

 ventral surface C. occidentalis, p. 76. 



1 Known only from Stimpson's original description Proc. Acad. Nat. Sci., 

 Philadelphia, p. 160, 1857. 



