from the Island of Malta. 109 



Echinus Duciei, Wright. PL IV. fig. 2. 



Test circular, much depressed : ambulacral areas more than half 

 the width of the interambulacral, with two rows of marginal, 

 nearly equal-sized tubercles throughout, and two other rows 

 within these, extending from the border to the mouth ; one of 

 these inner rows ascends a short way above the border : inter- 

 ambulacral areas with eight rows of tubercles at the border, 

 diminishing to two rows above the others, disappearing or 

 becoming of secondary size ; from the border to the mouth, 

 the eight rows continue of uniform size : the pores are in 

 triple oblique pairs ; between each pair there is a slight ridge 

 of the test, which gives a singular zigzag figure to the pori- 

 ferous avenues : mouth large and decagonal, base flat : apical 

 disc of moderate size, but not preserved. 



Dimensions. — Height l^^ths of an inch ; transverse diameter 

 m inch. 



Description. — This beautiful Urchin has been thought to be 

 identical with the E. Scilla, Desmoul., and the one figured by 

 Scilla in pi. 13. fig. 1, pi. 25. fig. 1, and pi. 26. fig. A, B, of 

 his work*; but the number of tubercles on each of the plates 

 in our specimen differs from the Echinus e Messana of that 

 author, who has figured only one large tubercle on each plate 

 of that form. From E. Scilla it is certainly distinct, as we 

 know of no Urchin that is common to the cretaceous and 

 tertiary rocks. The test is circular, much depressed on the 

 upper surface and flat below ; the ambulacral areas are almost 

 y^ths of an inch in width at the border, where we count 

 four rows of tubercles ; the marginal rows are very uniform in 

 size and arrangement from the mouth to the disc ; the two in- 

 ternal rows are smaller, and continue from the border to the 

 mouth j one of these extends a short distance on the sides, but 

 on the upper half of the areas there are only the two marginal 

 rows : the interambulacral areas are y o^hs of an inch in width 

 at the border ; there are eight rows of tubercles at this point 

 and onwards towards the base, they are nearly of the same size ; 

 but, from the border to the apical disc, the second row, from 

 the ambulacral areas, alone possesses the size the tubercles have 

 at the border ; the tubercles in the others diminish in size, and 

 disappear as the areas become narrower ; above, we find only 

 two marginal tubercles of the primary size, and internal to 

 these, a few of secondary magnitude irregularly set : all the 

 tubercles are raised on mammillary eminences, with areolas 

 around their bases, and numerous large granules fill up aU the 



* De Corporibus Marinis Lapidescentibus. 



