ASTEROIDEA 95 



The type measures R 37 mm., r 6-5 mm., R = 5"5 r. The present specimen measures 

 R 100 mm., r 20 mm., R = 5 r. Its large size is therefore remarkable. Comparison of 

 this specimen has been made with one from the type locality and there are no differences 

 which cannot be attributed to the disparity of size. 



The central enlarged spinule of paxillae is present all over the abactinal area. Some 

 plates of disk have 3 or 4 of these. Of the smaller secondary spinelets, there may be 20 

 co-ordinated in a convex group on larger plates of disk while much smaller interpolated 

 secondary plates have only 5 or 6, and no enlarged spinule. The superomarginal plates 

 carry a single, sharp, subconical spine 3 mm. long at base of ray. Proximal infero- 

 marginals with a similar, lateral, spine 4-5 mm. long; and on actinal surface of plate, 

 3 or 2 successively smaller spines in a transverse series. Distally these accessory 

 marginals are usually 2, then i. The secondary spinelets are very slender, spaced, and 

 lengthened adjacent to the principal spines. 



Similar, slender, spaced, spinelets cover the actinal interradial area, the plates of 

 which form about 4 chevrons with some extra plates adjacent to first inferomarginals. 

 Plates of innermost row extend to fourth inferomarginal. Most of actinal plates with 

 I or 2 enlarged central spinules. 



Adambulacral plates with a prominent furrow margin as described and figured by 

 Sladen. Six or seven spinelets can be assigned to this angular margin, but the same series 

 is continued along the adoral transverse edge of plate by 4-6 additional, similar spinelets. 

 The actinal surface is occupied by the broadened bases of the subambulacrals, which 

 vary from 2 to 4, are robust, about 3 mm. long, slightly tapered beyond the base, and 

 are bluntly pointed ; or, in the case of the second from furrow, subclavate with com- 

 pressed, subtruncate tip. 



The combined mouth-plates form a broad subtruncate projection nearly as broad as the 

 length of interradial dimension. On the broad actinostomial margin are 6 stout, 

 tapered, flattened spines (3 to each plate), the central pair about 3 mm. long. On the 

 furrow margin, continuing this series, are 4 much smaller spines. The actinal surface is 

 occupied by about 8 or 9 prominent tapered acute spines. 



The papularium of each ray is perfectly flat, for which reason its extent is not easy to 

 determine from the outside. It is strongly bilobed distally. Total length about 12 mm. ; 

 breadth 6-5 mm. ; length of each lobe 8 mm. Papulae small, well spaced. 



The dorsal muscle bands are well developed, about 4 mm. broad, slightly spaced 

 from one another. The inner, truncate end is attached to abactinal wall opposite 

 ninth ambulacral ossicle. From the outer corner of this inner end a rudimentary 

 tendon connects with a thin specialized dorsal crest of eighth ambulacral ossicle. 

 This ridge is perceptibly higher than that of seventh or ninth plates. In this respect 

 Pontaster is more nearly like Cheiraster than Pectinaster. In the latter the tendon is 

 better developed. 



Pedicellariae are not present. 



Colour note. Disk and base of arms pale warm pink. 



Type locality. Challenger St. 311, oflF western coast of South America, near the 



4-2 



