from the Lias and Oolites. 169 



mammillary eminences have well-defined areolaSj the summits of 

 the mammse are deeply crenulated, and the tubercles are small 

 and widely perforated ; the areolas are confluent above and be- 

 low ; between the two rows of tubercles an elevated band extends 

 from the mouth to the apical disc, composed of from 4-G rows 

 of unequal-sized granules. When viewed at the equator with 

 the naked eye, this Urchin appears to possess only ten rows of 

 tubercles placed nearly equidistant from each other ; but when 

 examined with an inch object-glass under the microscope its 

 true structure is disclosed, — the narrowness of the ambulacral 

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

 granular band down the centre of the interambulacra, and 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'aii "^ 

 inch and a half in length. "?*^^' 



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

 nifera is likely to be mistaken are Diadema Mooreii 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 beeiil^ 

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

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

 is associated wtth Turrilites Valdani, D^Orbig., and Ammonites 

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

 in the lowest schist of the " Posidonienschiefcr 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. '• '; <'j^- *"^*/*^^ *^ 



History. — Described by Mr. Buckman under the iMm€ iBctemI? -^ 

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

 on the Floetzgebirge of Wiirtemberg ; it has been recently figured 

 by him in his ' Handbuch der Petrefactenkunde,^ under the name 

 Cidarites criniferus. f: -^-i:: ; r zvv-i in- 



