RETORT ON THE ASTEROIDEA. 477 



Colour in alcohol, greyish white. 



Locality— Station 144a. 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 Rctaster, Perrier. 



Retaster, Perrier, Nouv. Archives Mus. Hist. Nat., 1878, 2e Serie, 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 Eetaster. 

 a. Geographical distribution : — 



Atlantic : 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. '"'Rctaster 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. 

 Southern 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). 

 Pacific : 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. 



