128 SYNAPTIDAE. 
Only twenty-three wheels were suitable for counting the marginal teeth and in 
ae iene great diversity, the number ranging from twenty-one to thirty; 
the average number per wheel is a trifle more than twenty-four, or just about 
twice the number of spokes; the largest relative number is twenty-seven teeth 
for ten spokes and the smallest is twenty-two teeth for thirteen spokes. Hub 
of wheel small and solid, its diameter .20-.25 of wheel diameter. Wheels range 
from 190 to 315 » across with the marginal teeth 30-50 u long. 
Station 4647. Eastern Tropical Pacific, 4° 33’ S., 87° 42’ 30” W., 2,005fms. Bott. temp. 35.5°. Lt. gy. 
and br. glob. oz. 
Two specimens. 
The oceurrence of two species of Myriotrochus south of the equator and 
at a depth of over two thousand fathoms is one of the most extraordinary 206- 
logical discoveries made by the ALBATROsS during her 1904-1905 cruise. The 
genus has not hitherto been known south of Norway, Newfoundland, Alaska, 
and northern Japan, nor at a depth of more than a few hundred fathoms. The 
species taken at station 4647 are very different in general appearance from any 
of the known forms, but giganteus is much like the common subarctic species 
rinkii in the character of its wheels. The wheels of giganteus average a trifle 
larger than in rinkii but the difference is insignificant. The spokes, however, 
are noticeably fewer (10-14, average almost twelve, as against 12-22, average 
seventeen) and much wider, while the hubs are larger (.20—.25 wheel-diameter 
as against about .16). The marginal teeth are relatively more numerous in 
giganteus, where they average almost exactly double the number of spokes. 
The wheels in bathybius are conspicuously different from those of any other 
member of the genus. Both the tropical species seem to be much larger and 
stouter than rinkii, the largest of the previously known species, although there 
is not great difference in length, since Ostergren reports specimens of rinkit 
up to 70 mm. long in life. The superficial resemblance of giganteus in form and 
color to a Molpadia is very striking and only the examination of the calcareous 
particles proves how misleading the resemblance is. 
It was hard to convince myself that the holotype of bathybius was not 
merely an aberrant individual of giganteus, but the wheels are too markedly and 
consistently different to support such an idea. Moreover the differences in the 
digitation of the tentacles and in the calcareous ring cannot be ignored and no 
other conclusion seems possible than that these two closely-allied species live 
together on the ooze in the great depths of the eastern Pacific. It is an 
environment peculiarly suited to holothurians, as is well shown by the fact that 
nine different species were taken in the single haul of the trawl at station 4647. 
