REPOET ON THE ASTEROIDEA. 531 



invisible without microscopic preparation ; they bear fasciculi of minute spinelets enve- 

 loped in a membranous sac, which causes them to appear like little semiglobular bag3 

 only. These sacculi are arranged with great regularity on each side of the median radial 

 line in obliquely transverse Hues, which pass up to the adambulacral plates. Along the 

 median line of the ray is a band of smaller and irregularly disposed sacculi. 



Adambulacral plates large. Armature consisting of an obliquely transverse series of 

 spinelets united by membrane and forming a semicircularly curved fan. 



Mouth-plates with a prominent median keel. Armature consisting of: — (1.) A 

 marginal series of three or four mouth-spines webbed together, and about three smaller 

 ones not webbed together. (2.) On the actinal surface of the plate, two larger secondary 

 mouth-spines in membranous sheaths. The actinostome is very wide, and there is a 

 broad exposed buccal membrane. 



Madreporiform body situated in one of the interradial sulci, external to the dorso- 

 central valvular apparatus. Surface grooved with numerous rather coarse striations. 



Ambulacral tube-feet large and biserially arranged, with a large, fleshy, centrally- 

 invao;inated, button-like terminal disk. 



No pedicellariae of any kind are present. 



Remarks. — This remarkable and abnormal type of asterid is altogether unlike any 

 other form. Its general morphological structure appears to me to justify its inclusion in 

 the family Pterasteridse. Its aberrant peculiarities, however, necessitate in my opinion its 

 separation in a distinct subfamily. 



Chorology of the Genus Pythonaster. 



a. Geographical distribution: — 



Atlantic : One species between the parallels of 30* and 40* S. 



Pythonaster murrayi, off the coast of South America, east of 

 Buenos Ayres. 



/9. Bathymetrical range : 1900 fathoms. 



y. Nature of the Sea-bottom : Blue mud. 



Chorological Synopsis of the Species. 



