32 



other areae ; and similar transverse risings are observable over the whole 

 upper surface. The flat raised surface, on the posterior part, is raised 

 much above the rest. On this surface, ten sets of tubercles, lessening 

 as they approach the margin of the area, are obliquely disposed, in 

 two rows. On the two lateral raised surfaces, a like number of sets of 

 tubercles are disposed, so as nearly to form angles along the central line. 

 The rest of the surface appears to have been beset with numerous small 

 tubercles ; the larger of which, being connected at rather acute angles, 

 with the tubercles of the raised surfaces, form undulating lines, giving, 

 in many places, the figure of the letter W. From the ridges above 

 mentioned proceed the angles observable in the circumference of the 

 fossil ; and from the transverse risings, the surface of the shell is formed, 

 as it were, into numerous facets. This description of the recent echi- 

 nus will be found to apply very nearly to the fossil here represented : 

 the difference being only that which proceeds from the injurious changes 

 which the fossil has sustained. 



The inferior surface of the fossil is nearly destroyed ; but from Leske's 

 account, we learn, that it very nearly resembles that of Spat, pusillus, and 

 Spat, striato-radiaius. The mouth is oval and transvere ; the upper lip 

 not covering, nor much projecting over, the under lip. In the superior 

 margin of the narrow end is the transverse oval anus; and, in the infe- 

 rior margin, is a renifbrm area. 



Similar specimens are, I believe, rare. It has, however, been figured 

 by Aldrovandus, Mus. Met. p. 475; Scilla, Tab. xi. Fig. 1; and by 

 Allion, the editor of the French edition of Klein, and of the French 

 Encyclopedia. 



Spatangus depresms, Tab. LI. Fig. 1, 2, Lesk. Under this species are 

 included those echinites which are of a flattened upper surface, of a 

 subrotund and cordated figure, proceeding from a dorsal groove, and 

 having five pair of ambulacral bi porous rows : one pair, in some varie- 

 ties, passing along the dorsal groove. The mouth is transversely placed 

 in the centre of the base, and the anus in the middle part of the nar- 



