from the Island of Malta. 95 



cated : anal opening high near the upper surface : apical disc 

 small and central. 



Dimensions. Antero-posterior diameter 2^ 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 Hemiasters. 

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

 considerable anteal sulcus, which measures \-fo 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 antcro-lateral ambulacra are rather 

 wider and much deeper than the single area ; they are l-j% 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 nearly 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 interambulacruin 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 

 the antero-lateral ambulacra, which are likewise slightly curved 

 forwards, in the length and depth of the posterior pair, which 

 equal the single ambulacrum in length, in the breadth and extent 

 of the peripetal fasciole, and the perpendicular truncature of the 

 posterior border, with the general tumidity of its sides, that it is 

 readily distinguished from them. 



Locality and stratigraphical position. It was collected from 

 bed No. 4, the calcareous sandstone at Malta, and is one of the 

 few tertiary Urchins in our cabinet ; it is the only specimen of 

 the species we have seen. 



