ALASKA NEMERTEANS. 9 



3. Six to 12 pouches of accessory stylets. Whitish, pinkish or flesh- 

 color P. carnea, p. 37. 



AAA. Body commonly rather short and thick. Proboscis sheath us- 

 ually reaches nearly or quite to posterior end of body. Pro- 

 boscis large ; central stylet well developed a 



a. Ocelli numerous, extending along the lateral nerves beyond the 

 brain. Basis of central stylet massive, with truncate or con- 

 cave posterior end Zygonemertes, p. 28. 



1. Each of the 2 pouches of accessory stylets contains about 5 stubby sty- 



lets. Olive green above and below Z. thatassina, p. 29. 



2. Each pouch of accessory stylets contains 2 or 3 moderately slender sty- 



lets. White Z. albida, p. 31. 



aa. Ocelli do not extend posteriorly beyond the brain. Basis of 



central stylet usually rounded posteriorly b. 



b. Body not very small. Ocelli usually numerous. 



Amphiporus, p. 40. 



1. Short and broad. Usually two pouches of accessory stylets with 5 to 



7 rather slender stylets each. Dark purplish or chocolate-brown 

 above, with a triangular white spot on each side of the head ; ventral 

 surface pinkish or flesh-color A.angulatus, p. 41. 



2. Basis of central stylet but half as long as the slender stylet itself. 



Usually 4 pouches of accessory stylets. Dorsal surface deep brown- 

 ish orange with 2 conspicuous oval or dark brown spots on head; 

 ventral surface pale orange or flesh-color A. bimaculatus, p. 44. 



3. Body rounded. Color of females yellowish orange, obscured in in- 



testinal region (in breeding season) by dark-green ova. Males 

 yellowish, with white flecks A. tigrinus, p. 46. 



4. Body rather broad and flat. Whitish, thickly mottled with dark brown 



blotches and dots; ventral surface whitish A. nebulosus, p. 48. 



5. Body slender, rather small. Ocelli usually 15-40. Usually 3 pouches 



of accessory stylets, with 2 or 3 stylets each. White. 



A. leuciodus, p. 51. 



6. Body extremely elongated for the genus. Ocelli usually 60-250, or 



more. Usually 6 to 12 (most commonly 8) pouches of accessory 

 stylets, with i or 2 stylets each A.exilis, p. 54. 



bb. Body very small. Ocelli few; usually 4 well-developed 

 ocelli arranged in a rectangle ; but sometimes these 4 eyes 

 are double or are fragmented into 4 groups of ocelli ; occa- 

 sionally ocelli are wanting Tetrastemma, p. 57. 



1. Ocelli 4. Brownish-red above, with median, white stripe; ventral 



surface white T. bicolor, p. 57. 



2. Ocelli of 4 groups, each consisting of several pigment spots of irreg- 



ular size. Pale yellow T. aberrant, p. 58. 



3. Ocelli wanting. Hermaphroditic. Whitish T. ceecum, p. 59. 



