128 THE APODOUS HOLOTHUBIANS 



Wheels few, usually less than 30, confined to anterior and posterior parts of dorsal 

 surface, 55-95 /^ in diameter, with 11-16 spokes and 17-26 teeth (plate vm, fig. 17). 



VITREUS 

 A A. Tentacles 10. Size very small, less than 20 mm. 



Calcareous rods present in tentacles; wheels of two sizes, with few intermediates, 



55-80 p. and 100-150 p., with 13-16 spokes and 18-26 teeth MINUTUS 



No calcareous rods in tentacles; wheels 130-225 /*, with 12-15 spokes and 24-30 teeth. 



THEELI 



MYRIOTRSCHUS RINKII. 

 PLATE VIII, PIGS. 21-22. 



Myrioirochus rinJcii Steenstrup, 1851, p. 55; pi. in, figs. 7-10. 

 Chiridota brevis Huxley, 1852, p. ccxi. 

 Myriotrochus rinkii Theel, 1877, p. 2: pi. i. 



LENGTH. 40-65 mm., the diameter one-fourth or one-fifth as much. 



COLOE. In life, "half-transparent" and "red" like " Synapta inhcerens" 

 (Ostergren) ; alcoholic material is whitish, yellowish, or greenish. 



DISTRIBUTION. Reported from numerous stations between Bering Sea on 

 the west to about 71 E. long., north to at least 82 N. lat., and south (on the 

 east coast of North America) to at least 45 N. lat., but on the Scandinavian 

 coast not south of 70 N. lat.; also reported by Theel ('86a) from the north- 

 ern coast of Asia, so that there is good reason to believe the species is really 

 circumpolar. The bathymetric range is from 2 to 666 meters. 



REMARKS. Although this species has such an extensive range, it exhibits 

 comparatively little variation. Ostergren (:03), in his interesting account of 

 this species, points out that in the most northerly specimens the number of 

 spokes is 70-80 per cent of the teeth, while in southern examples it is only 

 54-60 per cent. (See antea, p. 30.) In high arctic regions this species is 

 sometimes found in water only 2 or 3 m. deep; usually, however, from 5-100 

 m., and in the southern part of its range it occurs chiefly at depths of from 60 

 to more than 300 m. Nothing is recorded of its habits except Ostergren 's state- 

 ment that it shows "only a little tendency to autotomy." 



MYRIOTROCHUS VITREUS. 

 PLATE VIII, FIGS. 15-20. 



Oligotrochus vitreus M. Sars, 1866, p. 200. 

 Myriotrochus rinkii Auct., 1877-1898, partim. 

 Myriotrochus vitreus Ostergren, 18986, 1903. 



LENGTH. Up to 60 mm. 



COLOR. Perfectly transparent in life, with sometimes a greenish or (near 

 ends of body) reddish tinge; alcoholic specimens are less transparent. 



DISTRIBUTION. Reported only from coast of Norway, from Skager Rack to 

 Skraawem, in depths of 100-700 m. (Ostergren). 



