from the Island of Malta. 87 
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. 
Brissus latus (Wright, n. sp.). Pl. V. fig. 1 a-c. 
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 ;%,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 ;>ths of an inch 
from the anterior border; the large tubercles of moderate 
size. 
’ Dimensions.—Antero-posterior diameter 451, inches, transverse 
diameter 3%, inches ; height at the vertex | 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 
right angles with the longitudinal axis of the test ; the postero- 
lateral pair are directed obliquely backwards at an angle of 55°; 
both pairs lie in rather deep valleys, and the poriferous zones 
contain from twenty-eight to thirty pairs of pores in each avenue. 
The peripetal fasciole (1 a) makes an angular zigzag track, closely 
embracing the apices of the ambulacral areas. In the space which 
it bounds on the fore part of the shell, having for its base the 
antero-lateral areas, and its apex the anteal sulcus of the single 
ambulacrum, a number of large perforated tubercles set on cre- 
nulated eminences are arranged in groups (1c), the areolas of these 
tubercles are surrounded by small granules, and amongst them 
smaller tubercles are interposed; a few large tubercles occupy 
the angles between the apices of the antero-lateral and postero- 
lateral pairs, and likewise in the angle formed between the pos- 
VOL. H. ; H 
