94 PROCEEDINGS OF THE NATION.YL MUSEUM vol.86 



KEY TO POLYCLADS REPORTED FROM THE EASTERN COAST OF 



NORTH AMERICA 



1 (40). Without ventral sucker or marginal tentacles — suborder Acotylea, 2 



2 (21). With marginal eyes; male genital organs directed pos- 



teriorly, no cirrus ; nuchal tentacles present or absent ; 



uteri never fuse anterior to pharynx section Craspedommata, 3 



3 (6). Nuchal tentacles absent (or rudimentary) ; pharynx long, 



central, frilled ; 1 or 2 genital openings close to pharynx, 

 and not near posterior end; large muscular penis; no 

 vagina bulbosa family Discocelidae, 4 



4 (5). Color gray, with radiating light streaks and a lighter 



median band ; cerebral and tentacular eyes in 2 pairs 



of groups; Florida, North Carolina Discocelis grisea, new species 



5 (4). Color yellowish brown, with or without darker median 



band ; cerebral and tentacular eyes tend to form 3 

 pairs of groups ; Connecticut, Massachusetts. 



Discocelis mutabilis (Verrill, 1873) 



6 (3). Nuchal tentacles present 7 



7 (10). With 3 genital openings; penis unarmed and without 



sheath ; nervous system reddish in life family Latocestidae, 8 



8 (9). Size large, 20-25 mm by 10-15 mm; color yellowish, pale 



over pharynx ; Rhode Island, Massachusetts. 



Trigonoponis folium (Verrill, 1873) 



9 (8). Size small. 12-15 mm by 6-8 mm; color yellowish or pink- 



ish ; Cape Cod, 25 fathoms Trigonoporus dendriticus Verrill, 1893 



10 (7). With 2 genital openings; body broad or slender oval, 



firm ; eyes around all or part of margin ; tentacular 

 and cerebral eye groups present but sometimes diffuse ; 

 nuchal tentacles large, small (or absent in non-American 

 species); pharynx central and frilled; male genital 

 system directed posteriorly; prostate gland, separate; 

 ejaculatory duct opens into prostate duct or separ- 

 ately ; no vagina bulbosa family Stylochidae 



Female genital opening near posterior end and near that 

 of male; female system without Lang's vesicle, genlto- 

 intestlnal vesicle, or vaginal duct; nuchal tentacles 

 present subfamily Stylochinae, 11 



11 (12). With 2 clearly separate genital openings at least a seventh 



of body length from posterior end genus Stylochus, 13 



12 (11). With genital openings very close together and less than 



a twentieth of body length from posterior end. 



genus Eustylochus, 19 



13 (14). Body when extended 30-40 mm long and 10-12 mm wide, 



rounded at ends; pharynx mostly anterior to middle, 

 mouth at end of anterior third; color yellowish brown, 

 with numerous transverse light stripes, sometimes with 

 a light median band ; usually in Busycon shells ; New 

 England, North Carolina Stylochus zebra Verrill, 1882 



14 (13). Body when extended not more than three times as long as 



wide; mouth and pharynx near middle; not trans- 

 versely striped 15 



