KEPOKT ON THE ASTEROIDEA 133 



Synopsis of the Species included in the Genus Porcellauaster herein described. 



A. One cribriform organ in each interbrachial arc. Adambulacral plates with two 

 or three spines. No segmental pits or papillae. 



a. Eays short. Abactinal membrane with spinelets confined to limited areas . cxruleus. 



b. Rays long. Abactinal membrane entirely covered with spinelets. 



a. Rays tapering. Spines on each supero-marginal plate, long and 



delicate. Terminal plate small, with five spines. Spinelets 



of disk clavate ......... caulifer. 



b. Rays broad and robust. Spines on two plates only, stout. Terminal 



plate large and tubercular, with three spines. Spinelets of 



disk cylindrical ......... tuberosus. 



B. Three cribriform organs in each interbrachial arc. Adambulacral plates with one 

 spine. Segmental pits and papillae present. 



a. Rays long and robust. Abactinal membrane entirely covered with spinelets. 



Spines on each supero-marginal plate, long and thick . . . crassus. 



b. Rays short and delicate. Abactinal membrane with spinelets confined to 



limited areas. No spines on the supero-marginal plates or only rudi- 

 mentary ........... gracilis. 



Porcellanaster eremicus is not included in the foregoing table on account of its very 

 immature condition. To place the characters presented by such an early phase of growth 

 in comparison with those pertaining to the adult stage of the forms above mentioned 

 would clearly be not only useless but misleading. 



Two species of Porcellanaster are "named" by M. Perrier 1 amongst the material 

 dredged by the " Talisman," but no description has been published. The forms conse- 

 quently cannot be recognised. 



Clwrology of the Genus Porcellanaster. 



a. Geographical distribution : — 



Atlantic : Two species between the parallels of 50° N. and 40° S. 



Porcellanaster cserxdeus off the eastern coast of the United States 

 of America. Porcellanaster eremicus midway between the Cape of 

 Good Hope and the Island of Tristan da Cunha. 



Pacific : Three species between the parallels of 40° N. and 40° S. 



Porcellanaster tuberosus off the coast of Japan, south of Kawatsu. 

 Porcellanaster crassus in the mid south Pacific, near the meridian 

 of 135° W., approximately midway between Sydney and Valparaiso. 

 Porcellanaster gracilis off the western coast of South America, 

 between Valparaiso and the Island of Juan Fernandez. 



1 Comptes rendus, 1885, t. ci. p. 886. 



