mw^^hmfrom the Island of Malta. 161 



author of several memoirs on the palaeontology of the carbo- 

 niferous rocks of Belgium. 



Genus Brissus (Klein, 1734). • 



Form oval; the ambulacral summit excentral, and situated 

 near the anterior border ; the antero- and postero-lateral ambu- 

 lacral areas straight, and lodged in shallow depressions of the 

 test ; the anterior pair are nearly transverse, the posterior pair 

 deviating slightly from the longitudinal direction. The single 

 ambulacrum very simple in structure ; no anteal sulcus ; the 

 peripetal fasciole very sinuous ; mouth large, labiate, and near 

 the anterior border ; anal opening large, situated in the middle 

 of the posterior surface ; the subanal fasciole approximated close 

 to the anus. Four genital pores, the anterior pair smaller and 

 nearer each other than the posterior pair. The madreporiform 

 tubercle situated between the posterior genital openings ; five 

 perforated ocular plates placed before the genital pores and alter- 

 nating with them. This genus contains a greater number of 

 living than of fossil species ; the existing forms are limited to 

 the seas of warm latitudes ; the fossil species are found only in 

 the tertiary rocks. ,„(^ ..^^^ .^^ ^ jjio^liidms biol 



':i!..r,.u>- '' ■■''-'" ■'■■' ■ '^-^med 



: auolnB^^issus latus (Wright, n. sp.). PI. V. fig. 1 «-c. | haR 



Test convex and much depressed above ; transverse and antero- 

 posterior diameters nearly equal ; ambulacral areas of nearly 

 equal length ; the single ambulacrum lodged in a deep anteal 

 sulcus ; antero-lateral pair curved gently forwards ; peripetal 

 fasciole very zigzag and angular ; apical disc y^ths of an inch 

 before the centre of the disc ; base slightly convex ; sternal 

 process of the single interambulacrum raised before the anus, 

 having a central elevated ridge and numerous large tubercles 

 arranged in regular order on its surface ; subanal fasciole 

 enclosing a space 1/^ inch in diameter; anus situated in an 

 oblique truncation below the margin ; mouth y^^ths of an inch 

 from the anterior border; the large tubercles of moderate 

 size. 



IB 



Dimensions. — Antero-posterior diameter 4^^^ inches, transverse 

 diameter 3y^^ inches ; height at the vertex 1 inch. 



Description. — This Brissus is readily recognized by its broad 

 and depressed dorsal surface ; the ambulacral areas form deep 

 depressions in the test ; the single ambulacral area lies in an in- 

 considerable valley on the dorsal surface, but forms rather a deep 

 anteal sulcus ; the antero-lateral pair curve gently outwards and 

 forwards, forming an angle of 21°, with the transverse line at 



