168 CIDABITES. 



spines are rubbed away, the body is of a brownish hue, and 

 has a highly ornamental appearance in consequence of the 

 very prominent tubercles. On each ambulacra] plate there 

 is one large tubercle with two smaller, one placed on each 

 side of it, one of them being among the pores. On each 

 inter-ambulacral plate there are, except towards the apex, 

 three large tubercles, the central one largest, and some- 

 times one or two smaller ones, besides some very small 

 ones which form irregular borders round the larger. On 

 each ovarian plate there are three very little tubercles, 

 forming a border round the anus on their upper margins. 

 The avenues of pores from the apex to very near the mouth 

 have five pairs of pores in each oblique row. The rows are 

 bent, and four of the pairs of pores are above the bend. 

 Near the mouth the number of pairs of pores in the rows 

 diminishes, first to four pairs and lastly to three. The 

 mouth is somewhat pentangular. The entire body of this 

 Urchin is usually round ; but in one specimen in Mr. W. 

 Thompson's collection it is pentangular. 



This species was first observed as British by Dr. Leach, 

 who, supposing it to be altogether undescribed, exhibited 

 it to the Wernerian Society under the name of Echinus 

 lithophagiis. That distinguished and much-lamented na- 

 turalist, Mr. E. T. Bennett, afterwards communicated an 

 account of it to the Linnsean Society, rightly referring it 

 to the Echinus lividus of Lamarck, but was unaware of its 

 prior discovery by Dr. Leach. The latter gentleman 

 named it lithophagiis, on account of its singular boring 

 habit. In many places where it is found it is seen inhabit- 

 ing cavities or depressions in rocks, corresponding to it in 

 size, and evidently formed by itself. Mr. Bennett describes 

 each cavity as circular, agreeing in form with the contained 

 Urchin, and so deep as to embrace more than two-thirds 



