from the Island of Malta. 93 



Malta so well exhibits the distribution of the various beds with 

 their faults aud denudation. 



ISrissopsis crescenticus (Wright, n. sp.). PL VI. fig. 2 a-c. 



Test oblong, rounded before and truncated behind ; flattened on 

 the dorsal surface, and deeply indented by the ambulacral 

 areas ; the ambulacrum forms an anteal sulcus ; the anterior 

 and posterior ambulacra on each side form two lateral crescents 

 that abut at the longitudinal line ; the antero-lateral pair are 

 the longest and widest, they curve forwards and backwards, 

 and the posterior pair curve backwards and forwards; the 

 anterior pair form an angle of 45, the posterior pair an angle 

 of 65 ; the apical disc lies in a depression formed by the 

 confluence of the apices of all the ambulacra ; the posterior 

 border is squarely truncated, with the anal opening in its 

 upper angle ; the base is convex, with few tubercles and wide 

 naked spaces formed by the basal portions of the ambulacra; 

 the mouth is situated in the anterior third. 



Dimensions. Antero-posterior diameter 1 T 6 ^ inch, transverse 

 diameter l T 4 <j inch, height T 8 ^ths of an inch. 



Description. The most remarkable feature in this species 

 consists in the mode of arrangement of the ambulacra ; the ante- 

 rior and posterior areas of each side curve in opposite directions 

 and form crescents, the convexities of which are directed towards 

 the middle line of the test, and give value to the name proposed. 

 The antero-lateral pair form an angle of 45; they are about 

 the same length as the posterior pair, but are a little broader 

 and are more divergent : there are nineteen pairs of holes in the 

 external zone, and fourteen in the inner; the posterior pair 

 are nearly parallel with each other, and have a slight curve for- 

 wards to form the posterior horn of the crescent ; they are not 

 so much developed as the anterior pair ; the external zone of 

 holes contains fifteen pairs, but the inner zone (2 c) is imperfectly 

 developed, from their close approximation to those of the oppo- 

 site area : the apical disc is small ; the four genital holes are 

 large, the anterior pair being more closely approximated than the 

 posterior pair ; it is situated nearer the anterior than the posterior 

 border and lies in a confluent depression, in which the apices of all 

 the areas freely converge. The single ambulacrum is rather longer, 

 but not so wide as the anterior pair ; its lateral row of single holes, 

 with their accompanying tubercles, are small and indistinctly 

 seen, and it forms an inconsiderable anteal sulcus : the posterior 

 border is squarely and obliquely truncated, and in its upper part 

 near tin- dorsal surface is the large anal opening: the base is 

 rather convex; the sternal portion of the single interambu- 



