REPORT ON THE ASTEROIDEA. 477 
Colour in alcohol, greyish white. 
Locality.—Station 1444. Off Marion Island. December 26,1873. Lat. 46° 48’0”S., 
long. 37° 49’ 30” E. Depth 69 fathoms. Volcanic sand. Surface temperature 41°-0 Fahr. 
Remarks.—This species is remarkable for the manner in which it simulates the struc- 
ture of Retaster in the character of the supradorsal membrane and also, though to a less 
degree, in the character of the web and of the investment of the spines constituting the 
adambulacral armature. These points distinguish Pteraster semireticulatus from all other 
species of Pteraster with which I am acquainted. 
Genus Retaster, Perrier. 
Retaster, Perrier, Nouv. Archives Mus. Hist. Nat., 1878, 2e Série, t. i. p. 56. 
Diplopteraster, Verrill, Amer. Journ. Sci. 1880, vol. xx. p. 400. 
Although the differences which separate Retaster from Pteraster are comparatively 
slight superficially, their constancy and their morphological significance appear to me to 
justify generic recognition. If I am right in referring Pteraster multipes to this genus 
(as I think I am) the name Diplopteraster, proposed by Verrill, will fall as a synonym of 
later application. 
Chorology of the Genus Retaster. 
a, Geographical distribution :— 
AtLantTic: Three species between the parallels of 70° N. and 60° S. 
Retaster multipes, off the coasts of Norway and North America, 
extending as far south as Cape Hatteras. Retaster capensis, from the 
Cape of Good Hope. *Retaster verrucosus, near the entrance to the 
Strait of Magellan. 
INDIAN OcEAN : One species between the parallels of 0° and 30° S. 
Retaster cribrosus from Zanzibar and Mozambique ; and extend- 
ing to the Philippine Islands. 
SourHERN OcEan: One species between the parallels of 45° and 55° S. 
*Retaster peregrinator, from Kerguelen Island, 
EasTERN ARCHIPELAGO: Two species between the parallels of 20° N. and 20° S. 
Retaster cribrosus, from the Philippine Islands and extending into 
the Indian Ocean to the east coast of Africa. *Retaster insignis from 
Torres Strait and the Banda Sea, and extending to Port Molle (fide Bell), 
Paciric: Two species between the parallels of 20° and 60° S. 
*Retaster gibber, off the western coast of Patagonia. *Retaster 
insignis, off Port Molle (fide Bell), and extending into the Eastern 
Archipelago. 
