from the Island of Malta. 91 



of the base are intermediate in size ; the basal tracts of the am- 

 bulacral areas are destitute of tubercles; as they approach the 

 mouth they are again perforated with a single row of holes ; 

 those of the antero-laterals extend as far as the border, whilst 

 the single and posterior pair have only two or three pairs of their 

 plates perforated. 



Genus BRISSOPSIS (Agassiz, 1840). 



Form elongated, subcylindrical ; ambulacral areas straight, 

 short, and wide, converging near the summit of the test ; peri- 

 petal fascicle flexuous, closely surrounding the ambulacral areas; 

 two or four genital pores, the posterior larger than the anterior 

 pair; five ocular plates disposed nearly equally apart in a penta- 

 gonal form around the genital openings; subanal fasciole wide, and 

 situate at a considerable distance below the anal opening ; single 

 ambulacrum lodged in an anteal sulcus ; the basal portions of the 

 ambulacra are wide and naked ; the tubercles are very uniform 

 in size, and are crenulated and perforated. Three living species ; 

 the rest are fossil in the tertiary rocks. 



Brissopsis Duciei (Wright, n. sp.). PL VI. fig. 1 a-e. 



Test oblong, depressed anteriorly, elevated posteriorly ; apical 

 disc central ; ambulacral areas forming concave depressions ; 

 single ambulacrum the longest and widest ; antcro-lateral pair 

 straight, angle of inclination 34; postero-lateral shorter, angle 

 of inclination 55 ; peripetal fasciole broad and undulating ; 

 anus oval, large, situated high on the border ; base concealed ; 

 dorsal tubercles small, nearly of a uniform size, except on the 

 sides and the anterior part, where they are larger. 

 Dimensions. Large specimen. Antero- posterior diameter 

 3^ inches, transverse diameter 3 T 2 ^ inches : height cannot be 

 accurately measured. 



Small specimen. Antero-posterior diameter ly 9 ^ inch, trans- 

 verse diameter 1^ inch; height over the middle of the single 

 ambulacrum y^ths of an inch, at the highest point of the dorsal 

 region ly 1 ^ inch. 



Description. This beautiful Urchin is one of the most typical 

 forms of the group to which it naturally belongs. The test is 

 oblong and inclined, from the height of the anterior third being 

 less by y^ths of an inch than the posterior third ; the ambu- 

 lacral areas are all well developed, and arranged in the form of a 

 St. Andrew's cross; as the apical disc is situated near the centre 

 of the body, the regularity of their arrangement forms a con- 

 spicuous character of this species. The anterior ambulacrum (1 a) 

 is concave, and makes an inconsiderable anteal sulcus; there is a 



