from the Island of Malta. 265 



ambulacra diverge nearly straiujht outwards at an anale of 14"; 

 they form deep depressions in the test ly'^j ineh in length, and 

 the zones contain thirty pairs of holes in each : the postero- 

 laterals are slightly petaloid, and gently tiexed outwards ; they 

 are A^ths of an inch in length, and diverge at an angle of 60°. 

 The zones contain about twenty pairs of holes ; the test being 

 nearly as broad as it is long across the termination of the an- 

 tero-lateral ambulacra ; the anterior border is gently rounded, 

 and has a rather deep anteal sulcus for the ambulacrum ; from 

 the same point to the posterior extremity it tapers suddenly, 

 which gives a wedge-shaped appearance to the test when viewed 

 from above. The most remarkable feature in this Urchin is the 

 curious form which the single interambulacrum assumes, owing 

 to the great development of this area ; the dorsal surface forms an 

 inclined plane having an inclination of 17°; the anterior part is 

 therefore very much depressed, and the posterior part much ele- 

 vated. The single interambulacrum forms a prominent beak- 

 like process, beneath which the posterior border is broad, and 

 inclined downwards and forwards ; the sternal portion of this 

 area is prominent and convex, towards which the basal parts of 

 the lateral interambulacra slope suddenly forwards and inwards. 

 The anus is pyrifoi-m, and placed high up underneath the beak- 

 like process. The mouth is situated near the anterior border; it 

 has a large under-li]), but is crushed in the small specimen, and 

 covered up in all the others before us. The small apical disc lies 

 concealed at the posterior third of the dorsum by the prominent 

 apices of the lateral interambulacra. The peripetal fascicle takes 

 a zigzag course along the outer borders of the ambulacra, and 

 from the base of the antero-laterals it passes nearly at right 

 angles across the anterior interambulacra to the external side of 

 the single ambulacrum, where it makes another angle, then 

 passes down the side thereof y^ths of an inch, dips into the sul- 

 cus and unites with the opposite faseiole. The lateral faseiole 

 commences at the angle near the base of the antero-lateral am- 

 bulacra, and passes downwards and backwards nearly in a straight 

 line over the angle of the posterior border at some distance from 

 the anus, and meets the one from the opposite side, at the 

 middle line near the base ; in the triangle thus formed, the caudal 

 process and anus occupy the base, and a depression lies beneath, 

 which is filled with tubercles somewhat larger than those on the 

 dorsum, but smaller than those on the base; the tubercles are 

 perforated and raised on prominent crenulated bosses (fig. 3 c) ; 

 the sternal and basal portions of the test, as well as the anterior 

 border, being furnished with much larger tubercles. 



Affinities and differences. — The straightness of the pairs of 

 ambulacra, and the narrowness of the single anterior ambulacrum. 



