from the Island of Malta, 187 



Affinities and differences. — Brissopsis Duciei is readily distin- 

 guished from the other forms of this genus met with in the 

 Maltese beds, by the full development of its ambulacral areas, 

 their straightness, width and depth. The double crescent formed 

 by the ambulacral areas in B. crescenticus is a sufficient character 

 by which it may at a glance be distinguished from B. Duciei. 



Locality and stratigraphical position, — This species was col- 

 lected from bed No. 1, the Gozo marble, at Malta, where it is rare ; 

 the two specimens before us are the only ones we have seen. 

 We dedicate this fine species to the Earl Ducie, whose valuable 

 collection of Maltese fossils has added to our previous knowledge 

 of the palaeontology of the island, and whose geological map of 

 Malta so well exhibits the distribution of the various beds with 

 their faults and denudation. 



Brissopsis 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. ^l owi-ytoawJ 



Dimensions. — Antero-posterior diameter ly^^ inch, transverse" 

 diameter ly% inch, height y%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 



