PENTAGONASTER ROBUSTUS. 73 



Genus— NYMPHASTER, Sladen, 188-5. (See p. 14.) 



4. Ntmphaster radtattts, n. sp. PI. XXV, figs. l,la,l b. 



Specific Characters. — Arms very much produced. R : r : : 150 mm. : 10 mm. 

 Supero-marginalia in contact almost the whole length of arm. 



Material. — The only specimen of this species, formerly in the collection of Mr. 

 J. Starkie Gardner, is preserved in the British Museum of Natural History (E. 375). 

 The plates have, unfortunately, disappeared from the disc. Practically all that 

 remains is the greater portion of one arm. 



Description. — At the base of the arm the supero-marginalia are oblong. Each 

 measures 2*8 mm. in breadth, 2 mm. in length, and 3 mm. in height. Distally 

 these plates become almost square. They are ornamented by small granules 

 which tend to run together transversally to the length of the arm (PI. XXV, 

 fig. 1), and articulations for spines and deep depressions for pedicellarige are also 

 present. They are about twenty-five in number. The infero-marginalia equal 

 in number and size and oppose the supero-marginalia. Further they are about 

 the same height in marginal view. 



The breadth of the arm at the fourth supero-marginal is 6 mm. 



Stratigraphical Position. — Lower Chalk. Locality uncertain. 



Genus— PENTAGONASTER, Unci: (See p. 24.) 



3. Pentagonaster robustus, n. sp. PI. XXI, figs. 2, 2 a. 



Specific Characters. — Disc covered with small rounded plates. Margin high. 

 Rays short, high and robust. R : r : : 2T5 mm. : 9*9 mm. The supero-marginal 

 plates meet along the median line throughout almost the whole length of the arm, 

 and form a broad border to the disc. Interbrachial arcs paraboloid. 



Material. — The only specimen of this species is the one here described, formerly 

 in the Mantell collection and now preserved in the British Museum of Natural 

 History (48085). The locality from which it was derived is stated rather 



