2 



BRITISH FOSSILS. 



perfection of the specimen and the casual examination which he had 

 been enabled to bestow upon it. Desirous of rectifying the error 

 before it might affect generahzations concerning the classification of 

 Echinoidea, I had the original example drawn in all its details 

 and engraved, and on a second visit of M. Haime to London, that 

 gentleman, on sight of more perfect evidence, at once candidly ad- 

 mitted the correction of his original description. Soon afterwards, 

 finding that my friend Dr. Wright having also met with this fossil, 

 was about to publish it as a new Acvosalenia under another name, 

 I communicated to him the engraving which illustrates this paper, 

 with the information of the appellation bestovved upon it by 

 M. Haime, and which was at once very properly adopted by 

 Dr. Wright, and appended to a full description of this species 

 published in the Annals of Natural History. Through the last- 

 named able naturalist I have been enabled to complete my analysis 

 of this curious and beautiful Echinite, by adding full particulars 

 and figures respecting the apical disk, and an account of the spines 

 belonging to it. 



The body of Acvosalenia decorata is remarkable for presenting 

 a pentagonal outline, the five angles being- made by the five 

 ambulacral segments, which are tumid and rounded, whereas the 

 interambulacral divisions are depressed and as if flattened. Above, 

 this urchin is depressed ; beneath, it is hollowed out. The inter- 

 ambulacral areas are, centro-laterally, two and a half times as 

 broad as the ambulacrals. The latter bear two rows of small 

 secondary tubercles, each row distant from the other, and placed 

 nearly or quite ma^rginally Avith resj)ect to the segment, and having 

 the tubercles belonging to itself also ranged at regular distances. 

 In an ordinary specimen there are about twenty ambulacral 

 tubercles in a row. They are perforate, and placed on more or less 

 distinctly crenulated bosses. The centre of each ambulacral segment 

 is occupied by a rather broad band of nearly equal granules. The 

 interambulacral segments are each composed of two series of plates, 

 each plate bearing a prominent and perforated primary tubercle 

 placed on the summit of a crenulated boss, surrounded by a smooth 

 depressed areola. The outer and inner margins of each plate are 

 occupied by a raised granulated space of some breadth, and that 

 portion of the outer space immediately bordering the areolae has 

 two or three minute secondary tubercles at regular distances rising 

 among the granules. The central granulated (sutural) space on 

 each interambulacral segment forms a broad and conspicuous un- 

 dulated band. Of the ten interambulacral tubercles in each vertical 



