300 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



adhaerens Studer, 18S4. Abh. K. Pr. Akad. Wiss. Berlin, p. 54. Indian Ocean, 



off west Australia, 45 fathoms, 

 constrictus Farquhar, 1900. Trans. N. Z. Inst., 32, p. 405. Pacific Ocean, off 



New Zealand, 

 sibogae Koehler, 1904. Opli. " Siboga," pt. 1, p. 165. Pacific Ocean, off Hal- 



malieira, Kei and Rotti Islands, Dutch East Indies, 113-605 fathoms, 

 japonicus Koehler, 1907. Bull. Sci. Prance et Belg., 41, p. 346. Pacific Ocean, 



off Japan, 

 papillatus Clark, supra. 



Key to the species of Ophiocreas. 



Radial shields and upper arm-plates free from spines. 



Skin of disc and bases of arms free from numerous pits and pores. 



Oral shields very small, concealed ; arms 5 ; 1 or 2 tentacle scales present on 

 third and commonly on second pair of pores. 1 

 Tentacle pores small, their diameter much less than distance between 2 

 consecutive pores. 

 Radial shield long, narrow, thick ; genital slits long, exceeding one-eighth 

 of diameter of disc. 

 First 5 or more (rarely only 4) tentacle pores with only 1 scale or none. 

 Skin thick, soft, and smooth ; radial shields long, meeting at centre 

 of disc. 

 Skin very thick, wrinkled ; no oral papillae or calcareous granules 



on mouth angles carnosus. 



Skin thick and minutely tuberculated ; small oral papillae or 



calcareous granules on sides of mouth angles . . . caudatus. 



Skin thin, provided on disc with minute granules ; radial shields 



short, not quite meeting at centre oedipus. 



First 2 or 3 (rarely 4) tentacle pores with 1 tentacle scale or none. 

 Oral papillae present, 9 or 10 to each mouth angle; skin of disc with 



numerous minute calcareous granules lumbricus. 



Oral papillae wanting; skin of disc perfectly smooth . . . sibogae. 

 Radial shields short, broad, thin, and flat ; genital slits very short, less 



than one-tenth the diameter of disc 2 abysslcola. 



Tentacle pores very large, their diameter about equalling distance between 

 2 consecutive pores. 

 No oral papillae ; skin of disc smooth ; genital slits long, converging 



japonicus. 



6-9 small rounded oral papillae on each side of mouth-slit ; skin of disc 



and bases of arms rough with numerous small calcareous granules ; 



genital slits short and nearly parallel papillatus. 



1 Not counting the buccal pair. 



2 In both the original description (1879) and the Challenger Report (1882) it is 

 said that the genital slits are " 5 mm. long," an obvious misprint for 0.5 mm., as 

 shown both by context and figures. 



