34 PEOCEEDINGS OF THE NATIONAL MUSEUM VOL.73 



Plate 3 



Petasiger nitidus, new species (continued) 



Fig. 11. Ventral view of head, in glycerine ; diameter, including spines, 0.49 mm. 

 The recurved dorsal spines in this specimen seem to be exceptional. 



12. Ventral view of another specimen ; diameter, including spines, 0.42 mm. 



13. Dorsal view of same. 



14. Transverse section at level of ventral sucker ; diameter 0.38 mm. pr. 



prostate gland. 



15. Transverse section at level of ovary, diagi'ammatic. 



16. Transverse section near posterior end ; diameter 0.20 mm. 



HimastJila elwigata (Mehlis), from Larus argentatus 



17. Ventral view ; length 6.30 mm. 



18. Ventral view of head in glycerine ; diameter, including spines, 0.36 mm. 



19. Postero-lateral spines, more highly magnified ; length of spine 0.054 mm. 



20. Female genitalia ; diagi'ammatic, from transverse sections. 



Plate 4 

 nimasthla incisa, new species, from Oidemia deglandi 



Fig. 21. Ventral view; length ^ mm. 



22. Anterior end of same; diameter at level of ventral sucker 0.6 mm. 



23. Oral spines, foreshortened, sketched from a transverse section ; Spencer 



6x/4 mm. 



24. Oral spines; longer spines 0.051 by 0.018, shorter 0.039 by 0.012 mm. 



25. Transverse section near anterior border of ventral sucker ; breadth 



0.43 mm. The section in front of this contained the genital pore. 



26. Transverse section at level of ovary ; breadth 0.74 mm. 



27. Transverse section immediately behind ovary ; partly diagi-ammatic, 



about four consecutive sections used ; breadth 0.8 mm. 



Plate 5 

 Himastlil<i incisa, new species (continued) 



Fig. 28. Transverse section at level of seminal vesicle ; breadth 0.67 mm. 



29. Transverse section near posterior end ; breadth 0.38 mm. 



30. Margin of body at anterior end of vitellaria ; average length of serra- 



tions about 0.02 mm. 



31. Margin of body at level of ovary ; length of serrations about 0.04 mm. 



32. Transverse section of body wall at level of seminal vesicle; Spencer 



6x/4 mm. ; eg. cuticular gland ; Ini. longitudinal muscle. 



33. Transverse section of body wall at level of ovary ; Spencer 6x/4 mm. 



Mesorchis pseudoechinatus (Olsson), from Larus argentatus 



34. Ventral view of body, lateral of head and neck ; length 5.32 mm. 



35. Dorsal view of slightly macerated specimen, from which all spines had 



disappeared ; length 4.48 mm. 



36. Ventral view of body, dorsal of head and neck ; length 3.5 mm. 



37. Ventral view of head, in glycerine ; diameter, including spines 0.42 mm. 



