from the Island of Malta. 189 



Hemiaster Grateloupi (Sismonda sp.). 



Syn. Schizaster Grateloupi, E. Sismonda, Echin. Foss. Piem. p. 27. 



tab. 2. 

 Hemiaster Grateloupi, Desor, Ann. Sc. Nat. torn. viii. p. 19. 



Test orbicular^ convex above and below, with tumid inflated 

 sides : the single ambulacrum short, shallow and narrow ; the 

 antei'o-latcrals long, deep and diverging; angle of inclination 

 25° ; the postero-lateral pair slightly curved inwards ; angle 

 of inclination 62^; both pairs lie in deep depressions : the peri- 

 petal fasciole broad and undulating : the single interambu- 

 lacrum forming a dorsal ridge : posterior border abruptly trun- 

 cated : anal opening high near the upper sui-face : apical disc 

 small and central. 



Dimensions. — Antero-posterior diameter 2y^o inches, transverse 

 diameter 3 inches, height 1^^^ inch. 



Description. — The orbicular form and inflated sides of this 

 Urchin, with its large, deep, diverging ambulacra, and greater dia- 

 meter in the transverse than in the longitudinal direction, impart 

 to it an air which widely distinguishes it from other Ilemiasters. 

 The single ambulacrum is narrow and shallow, and forms an in- 

 considerable anteal sulcus, which measures l-j^"^ inch in length 

 from the apex to the fasciole ; it has a single row of lateral 

 holes and accompanying tubercles of small size placed near each 

 other within, and the holes only at considerable distances apart 

 without the fasciole. The antero-lateral ambulacra are rather 

 wider and much deeper than the single area ; they are 1^-^ inch 

 in length, and are directed forwards and outwards, forming 

 an angle of 25°; the walls of the depression are formed by 

 the poriferous zones, and the base by the intervening smooth 

 space between them : the postero-lateral ambulacra are directed 

 obliquely backwards and gently curved inwards ; they are 1 inch 

 long and form an angle of 62^ : the peripetal fasciole closely 

 embraces the base of the areas, and maintains a neai'ly uniform 

 width throughout its course : the test is very much inflated an- 

 teriorly and laterally, and its posterior border is abruptly trun- 

 cated : the single interambulacrum is elevated into a ridge, 

 which rises between the two posterior ambulacra, at the termi- 

 nation of which the anal opening is situated : the test is covered 

 with small, nearly equal-sized tubercles, which are larger on the 

 fore-part, cheeks, and sides than elsewhere : the apical disc is 

 small, and lies in a depression at the centre of the test, the 

 apices of the interambulacra rising into little eminences around 

 it : the base is entirely concealed by the matrix. 



Affinities and differences. — This large species differs so much 

 from its congeners in its breadth, in the depth and divergence of 



