118 



ECHINOCYPHUS 



circles of large sub-elliptical granules, that are prolonged in a radiated manner towards 

 the base of the mammillon (fig. 2 d). The coronal plates at their lower border are 

 marked by a horizontal depression, as if the lower half of the plate had been scooped out 

 (fig. 2 a) at the expense of a portion of the granular circle. The boss is prominent, 

 and its summit is marked with feeble crenulations. The mammillon is always large and 

 unperforated. The miliary zone is wide in its upper part, and the surface of the plates is 

 covered with a very fine granulation ; at the ambitus it is filled with two or three rows of 

 large granules, which diminish below into a single series, and take a zigzag direction 

 towards the peristome. 



The small mouth-opening, about one third the diameter of the test, is lodged in a 

 concave depression (fig. 2 b). The peristome is circular, and nearly equally lobed, and 

 the incisions are slight. 



The apical disc, which is very rarely preserved (PI. XXII, fig. 4), equals the oral 

 opening in size, and is flat and finely granulated ; the cordate ocular plates are rather 

 large, and perforated close to the ambulacra! margin ; the large ovarial plates are per- 

 forated, and the madreporiform body occupies the right anterior plate ; the single posterior 

 plate is wanting. 



Afinities and Differences. — This species very much resembles Cyphosoma rotatum, Forb., 

 of which it proves to be a variety ; the irregularity of the two rows of ambulacral tubercles, 

 one of which is often abortive, is not, according to our observations, a persistent character, 

 and for this reason we regard E. difficilis and E. rotatm as varieties of one form. M. 

 Cotteau, however, considers them distinct, and takes as a diagnostic character the single 

 row of tubercles in the ambulacral areas, as this difference does not appertain to age, 

 seeing that it is found in small as well as in large specimens. Echinocyplius difficilis, 

 Ag., may be confounded with GlypJiocyjjJms intermedins, Cott., which has a similar dis- 

 position of the ambulacral tubercles, only that they are perforated in Glyphocyphus 

 and unperforated in Echinocyphiis. 



Locality and Stratiyraphical Position. — I have several specimens which I collected 

 from the hard Grey Lower Chalk near Folkestone, and numerous smaller examples from 

 the Upper Greensand near Warminster ; from the latter formation a very large specimen 

 was obtained, now in the cabinet of G. E. Sloper, Esq., Devizes. The late Dr. S. P. 

 \A'oodward states that it measures nine lines in diameter, and four and a half in height ; 

 l)oth rows of ambulacral areas are well developed, and the miliary granules form a 

 prominent framework to the tubercles. 



In France, M. Cotteau records this species from the Etage Cenomanien of Vellclaire 

 (Haute-Saone), and Presagny (Eure), where it is rare. 



History. — First catalogued as Biadema rottdare, Ag., from Durdle Door, Dorset, by 

 Prof. McCoy, in his ' Mesozoic Radiata,' in 1848, and afterwards by Prof. E. Forbes, as 

 Biadema rotatum, from the U{)per Greensand of Warminster, in the second edition 

 of the ' Catalogue of British Fossils.' 



