10 BULLETIN 100, UNITED STATES NATIONAL MUSEUM 
The specimen is not in a very good state of preservation; partic- 
ularly is it regrettable that all the primary spines of the oral side 
are broken, not one of them showing the skin bag enclosing the end 
of the spines. Still, there cannot be the slightest doubt of the correct- 
ness of the identification, the more so as I have had the type specimen 
for direct comparison. 
The specimen was completely collapsed and partly torn. But by 
stuffing it, as explained above, I made it assume its natural shape, 
showing the shape of the test to be low-hemispherical. 
Already de Meijere was in doubt whether this species could prop- 
erly be referred to the genus Phormosoma. The careful study of 
the two known specimens that I have been able to undertake shows 
conclusively that it represents a distinct generic type. The main 
characters distinguishing it from Phormosoma are these: The areoles 
of the oral side are not sunken; there is no marginal fringe, the 
tubercles of the oral side continuing without interruption on to the 
aboral side; the edge of the test is not sharp, as in Phormosoma. 'The 
outer demiplate of the ambulacra on the aboral side remains broadly 
in contact with the interambulacral edge, this last character being 
from a morphological point of view the most important. In the 
larger Albatross specimen the outer demiplates even increase so much 
in size as to exclude the primary plates from the edge of the area; as 
a matter of fact, we have here a many-plated condition of the am- 
bulacra directly comparable to that found in various Paleozoic 
echinoids.* 
Subfamily ASTHENOSOMINAE 
Genus TROMIKOSOMA Mortensen 
TROMIKOSOMA TENUE (A. Agassiz) 
Phormosoma tenue A. AGASSIz, Challenger Reports, Zoology, vol. 3, pt. 9, 
Echinoidea, p. 91, pl. 18; pl. 14; pl. 17a, fig. 8; pl. 18a, figs. 1-18; pl. 18b; 
pl. 1 18¢, figs. 5, 6, 8,9; pl. 19a, fig. 2; pl. 42, fig. 7; pl. 44, figs. 7-9, 1881. 
Echinosoma tenue MorTENSEN, Ingolf Echinoidea, pt. 1, pp. 56, 63, 177, pl. 12, 
figs. 35, 40, 1908; pt. 2, pp. 6, 21, 1907.—A. Acassiz and H. L. Crarx, 
Hawaiian and other Pacific Echini, Echinothuridae, p. 165, pl. 67, figs. 12-21, 
1909. 
Tromikosoma tenue MorTENSEN, Monograph of the Hehinoidea, vol. 2, p. 171, 
pl. 6, fig. 1; pl. 7, figs. 1-5; pl. 75, figs. 8-17, 1935. 
Locality.—Station 5636; Pitt passage; Gomomo Island (E.) bear- 
ing N. 46° W., 6 miles distant (lat. 1°55’00’’ S., long. 127°42’30”’ E.) ; 
2,307 meters; gray mud and fine sand; December 3, 1909. Three 
specimens. 
Remarks.—That these specimens are identical with the typical 7. 
tenue from off Japan is beyond doubt, and the occurrence in the Malay 
*Cf. Mortensen, Monograph of the Hchinoidea, vol. 2, p. 85, fig. 56, 1935. 
