20 Papers from the Marine Biological Laboratory at Tortugas. 



Key to the genera and species described in this paper. 



Heteracotylea : 



i. Body without tentacles elongate, paired anterior suckers 2 



2. Posterior sucking-disk unarmed and without radial ridges. . Udonella socialis 

 Posterior elongated disk provided with numerous small suckers 



Microcotylc incisa 



ASPIDOCOTYLEA : 



Large elliptical ventral sucker with numerous depressions, no oral 

 sucker, intestine not bifurcate ; one testis ; marginal sense-organs 



Aspidogaster r in gens 

 Deontacotylea : 



No suckers, mouth minute, intestine biramous, the rami with branches; 

 genital apertures separate at posterior end; body covered with 

 minute spines, oval Deontacylix ovalis 



Malacotylea: 



1. One sucker (oral) present (Monostomid.*) 58 



2. Two suckers present 3 



3. (a) An anterior sucker (acetabulum) and a small ventral sucker (oral) 



(Gasterostomid^e) 4 



(b) An anterior sucker (oral) and a small ventral sucker (genital) 



(SlPHODERID^S) 5 



(c) An anterior sucker (oral) and the acetabulum at the posterior end 



(Paramphistomid.^) 11 



(d) An anterior sucker (oral) and the acetabulum on the mid-ventral 



surface (Fasciolid^e) 13 



4. Gasterostomid.^. The species of the genus Gasterostomum could not 



be satisfactorily determined on account of the poor condition of 

 the material. See figures 217-225. 



5. SlPHODERIDvE 6 



6. Testes more than one 8 



One testis 7 



7. Esophagus short or none, body ovate Gcnolopa ampullacea 



Esophagus as long or longer than pharynx, body linear-oblong 



Gcnolopa truncata 



8. Testes two 9 



Testes more than two Siphodcra vinalcdwardsii 



9. Testes opposite, vitellaria compact 10 



Testes tandem, uterus in front of testes vitellaria diffuse 



Prodistomum gracile 



10. Ovary behind testes, body subglobular Stcgopa globosa 



Ovary between testes, body short-oval Metadena crassulata 



1 1 . Paramphistomid.* 12 



12. Lateral pharyngeal pockets and cirrus-sac present; no ventral papilla?; 



testes slightly lobed . . Cleptodiscus reticulatus 



13. Fasciolid^e 14 



14. Pharynx present 15 



No pharynx (immature) Distomum fenestratum 



15. Ovary behind testes 45 



Ovary in front of testes (beside testes in Dichadena, No. 43) 16 



16. Vitelline glands compact 42 



Vitelline glands diffuse or dendritic 17 



1 7 . Body smooth 22 



Body more or less spinose l 18 



18. Without oral spines 20 



With oral spines 19 



1 Spines, both those on the body and neck and those around the mouth, are often deciduous. 

 There may be cases therefore of really spined forms described as spineless. See for example fig. 87, 

 which is plainly near the genus Stephanochasmus , 



