from the Lias and Oolites. 25 



areas, the closeness and smallness of their rows of tubercles, the 

 granular band down the centre of the interambulacra, find the 

 unequal size of its component tubercles, alike contribute to make 

 the deception almost complete. 



The most remarkable parts of the structure of this tiny fossil 

 are the spines, which in some crushed specimens are preserved 

 in situ ; they are long, delicate and hair-like, and have large 

 articular heads ; these spines look like so many bristles laid down 

 in all directions upon some slabs of the Lias shales ; in a crushed 

 test of four-tenths of an inch in diameter the spines measured an 

 inch and a half in length. 



Affinities and differences. The only Cidarites for which A. cri- 

 nifera is likely to be mistaken are Diadema Moorei and Pedina 

 Etheridgii ; from the former it is easily distinguished by the nar- 

 rowness of the ambulacral areas and the smallness of the tubercles 

 thereof; from the latter it differs in the comparative smallness of 

 its ambulacral areas, and above all in having the mammillary 

 eminences of its tubercles deeply crenulated, a character which is 

 absent in all the Pedinas we know ; at present we know of no 

 other Urchin in the Lias for which it can be mistaken. 



Locality and stratigraphical range. A. crinifera has been 

 found only in the lower shales of the lower Lias near Lans- 

 downe, Cheltenham, and in the same stratum near Gloucester j it 

 is associated with Turrilites Valdani, D'Orbig., and Ammonites 

 oxynotus, Quenstedt. It has been collected by Prof. Quenstedt 

 in the lowest schist of the " Posidonienschiefer von Pliensbach 

 bei Boll " in Wiirtemberg. We have before us now two slabs 

 of this curious bed ; one surface of the slab is covered over with 

 the long hair-like spines strewed about in all directions, with 

 here and there the crushed test of one of these Urchins with its 

 spines attached and in situ. 



History. Described by Mr. Buckman under the name Echinus 

 minutus, but previously noticed by M. Quenstedt in his work 

 on the Flcetzgebirge of Wiirtemberg ; it has been recently figured 

 by him in his ' Handbuch der Petrefactenkunde/ under the name 

 Cidarites criniferus. 



Diadema Davidsoni, Wright. PL II. fig. 2, a-e. 



Test depressed, circular; tubercles elevated upon prominent 

 mammillary eminences ; pores in a single file throughout ; a 

 few small secondary tubercles in the interambulacra ; the pri- 

 mary ambulacral tubercles nearly as large as those of the 

 interambulacra. 



Height /fiths of an inch, transverse diameter 1 inch and / O ths. 

 Description. This beautiful Urchin has a regular circular 



