94 Dr. T. Wright on Fossil Echinoderms 



lacrum is slightly prominent, and ornamented with a few rows 

 of rather larger tubercles disposed in zigzag lines : the basal 

 tracks of the ambulacral areas are entirely naked, and where 

 they terminate around the mouth five petaloid poriferous radii are 

 observed. The mouth, of moderate size, is in the anterior third ; 

 the peripetal fasciole is narrow and indistinct ; the subanal 

 fasciole is much broader, and remote from the anus, but the test 

 is unfortunately broken in this region ; the tubercles are nearly 

 all of the same size, but a few larger ones occupy the sides, front, 

 and base. 



Affinities and differences. The flatness of the dorsal surface, 

 the deep depressions made by the petaloid portion of the am- 

 bulacral areas, and the double crescent formed by them, readily 

 distinguish B. crescenticus from its congeners. So few fossil 

 species of this genus have been figured or described, that we can 

 only compare it with the other forms obtained from the same bed, 

 from both of which it differs in many well-marked characters. 



Locality and stratigraphical position. It was collected from 

 bed No. 4, the calcareous sandstone at Malta, where it is rare. 



Genus HEMIASTER (Desor, 1847). 



Urchins with a high and much inflated test ; ambulacral sum- 

 mit nearly central ; the petaloid portions of the ambulacral areas 

 situated in depressions more or less deep ; the antero-lateral are 

 in general much longer than the postero-lateral pair; the peripetal 

 fasciole only surrounding in an angular manner the ambulacral 

 star. This genus differs from Micraster in all the species having 

 a more inflated body with a peripetal fasciole ; from Brissopsis in 

 having the postero-lateral ambulacra in general much shorter, 

 and the anterior and posterior pairs more unequal in length, 

 and likewise in having no subanal fasciole. A very few species 

 are found in the tertiaries, the majority belonging to the cre- 

 taceous rocks. 



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 

 antero-laterals 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 interatnbu- 

 lacrum forming a dorsal ridge : posterior border abruptly trun- 



