84 FOSSIL ASTEROIDEA. 



radialia and centrale. Major radius about four times the length of the minor 

 radius. Only radialia enter the base of the arm. Dorsal surfaces of arms flat, 

 sides slope away at an obtuse angle from this. Ossicles distinctly imbricating. 

 A few intermarginalia present. 



Material. — The only specimen of this species is preserved in the Brighton 

 Museum. The specimen consists of the disc and a portion of three arms. On the 

 whole little displacement of the ossicles has taken place. 



Description. — The disc is strongly convex, and is covered with the circlet of 

 primary radialia and interradialia which are disposed around the centrale. All 

 these ossicles appear shaped like a breast-plate. The centrale has a diameter 

 of 4"2 mm. The primary interradialia are larger, possessing a diameter of 

 5'3 mm., whilst the primary radialia are the smallest of the series, measuring only 

 3"7 mm. across. Between the centrale and the primary interradialia a number 

 of irregularly distributed plates appear. In the next right-hand interradius 

 to the madreporite a number of these appear to have surrounded an anal opening. 

 The primary interradialia almost touch one another, and the radialia consequently 

 rest on the bases of pairs of ossicles. A few adradialia are present, but they are 

 confined to the disc. A pair of them help to enclose the madreporite, which 

 is a polygonal plate 9 mm. in greatest diameter. The ornamentation of the 

 ossicles is rather coarse when present, but usually it is very much worn away. 



The arms are well produced. R : r : : 30 -f- mm. : 7'8 mm. They are 1*3 mm. 

 in breadth at the base. After the fourth or fifth radiale the remainder become 

 minute but persist throughout the length of the arm preserved. 



The supero-marginalia are finger-shaped ; they, as also the infero -marginalia, 

 distinctly imbricate. The dimensions of the third supero-marginal, reckoning 

 from the median interradial line, are as follows : length 2'3 mm., breadth 3 - l mm. 

 The long axes of the supero-marginal plates slope away distally, thus causing 

 pairs of plates to assume the shape of arms of a V. They are at least thirteen 

 in number. 



The infero-marginal plates are similar in size and number to the supero- 

 marginal series. In the interradii a few intermarginalia are present, These force 

 the supero-marginal series to the surface of the disc. 



Nothing is known of the ventral surface. 



Locality <nt<l Stratigraphical Position. — Upper Chalk, Woolwich. 



