BRITISH FOSSILS. 



3 



Those of the lower surface are two-tenths of an inch in length, slender, 

 tapering, smooth, longitudinally ridged with about eight ridges and 

 enlarged at the base, where they are surrounded by a crenulated collar. 

 Curious club-tipped pedicellaria-like bodies occur among them, which 

 may represent the spines of the miliary tubercles described as occurring 

 on the dorsal surface. 



Mr. Bowerbank has communicated the result of a microscopic exami- 

 nation of the spines of Galerites in his possession. He finds the small 

 dorsal spines of Galerites albogalerus to differ from those of suhrotundus 

 in being thickened at the base and set on the tubercles as it were 

 sessile, instead of being shortly pedunculated, as they are in the latter 

 species. The minute moniliform spines of G. albogalerus are xis- of an 

 inch in length and of equal diameter. Three were measured, and all 

 were as nearly as possible of the same size and proportions. They were 

 all perfectly smooth. 



The apex of the body is the highest point of the back. The apical 

 disk is formed of five genital and five ocular plates. Four of the former 

 are perforated for the oviducts in their lower halves ; one of the per- 

 forated plates is greatly enlarged above, to form the centre of the disk, 

 where it is wrinkled and punctured, constituting the madreporiform 

 plate. The fifth posterior and odd genital plate is very small, triangular, 

 and imperforate. The perforations of all are nearly marginal. 



The existence of a dental system in Galerites was made known by 

 Mr. Charles Stokes, who communicated his discovery to the Geological 

 Society. A second specimen with teeth adorns the collection of Mr. 

 Bowerbank, and in it the dental " lantern " is sufficiently protruded to 

 enable us to determine the form and structure of its principal elements. 

 The teeth are smooth, white, lanceolate, triangular, each consisting of a 

 concave lamina terminating below in the dental point, and strengthened 

 on its back by a prominent rounded ridge. In the " Catalogue Raisonne 

 des Echinides," the authors have by an oversight attributed as a 

 character to the Cassidulidce, the absence of a masticatory apparatus. 

 It is probable that all the members of that family had a dental system 

 similar to that of Galerites. The absence of traces of it in fossil speci- 

 mens must be accounted for in the same way in which we know the 

 absence of the dental lantern in dead specimens of existing Echini to 

 have been caused, viz., by the decay of the internal parts and the dis- 

 articulation of the segments of the masticatory apparatus. 



The following table of the relative dimensions of nine specimens, 

 among those in the collection of the Geological Survey, will give some 

 idea of the variable proportions in this species. 



