EllITISH 



FOSSILS. 



Decade IV. Plate YIII. 



ANANCHYTES (HOLASTER) PILULA. 



[Genus ANANCHYTES. Lamarck. (Sub-kingdom Radiata. Class Echinodermata. 

 Ordfer Echinoidea. Family Ananchytidse.) Body orbicular, oblong or obscurely cordate, 

 tumid, with homogeneous ambulacra convergent on the vertex, all plane or with the anterior 

 ambulacrum only lodged in a shallow furrow. No fascioles. Vent terminal, marginal or 

 supra-marginal. Apical disk elongated, and composed of four perforated genital and five 

 perforated ocular plates. Tubercles perforate, their bosses crenulate. Spines minute. 

 No dental apparatus. 



Subgenus Hol aster. Body subcordate, vent terminal, supra-marginal.] 



Diagnosis. A. amhitu vix cordato ; testa altd hcemisphcerica tumida 

 inferne planatd ; ano alto. 



Synonyms. Ananchytes pilula, Lamarck. An. sans Vert., vol. iii. p. 27. 



Spatangiis prunella f Mantell, Geol. Sussex, p. 193, pi. 17, f. 22, 23. 



Spatangus pilula, Desmoulins, Tabl. Syn. des Echin., p. 406. 



Ananchytes analis, Roemer, Norddeutsch. Kr. p. 35, pi. 6, f. 18. 



Holaster pilula, Agassiz, Cat. Syst. p. 1. Agassiz and Desor, Cat. 

 Raisonne des Echin., in Annales des Sc. Nat. 3d ser., vol. viii. p. 29. Forbes, 

 in Dixon's Geol. Sussex, p. 341, pi. 24. f. 10, 12 (junior). 



Holaster coravium f Forbes (not of Lamarck), in Dixon's Geol. Sussex, 

 p. 342, pi. 24, f. 7-9. 



Body oblong, lofty, always elevated, but not always to the same 

 degree, tumid above, flattened below, and with sharply angulated 

 sides, anteally obtuse and jflattened, posteriorly abruptly truncate, 

 vertex slightly in front of apical disk ; posteal interambulacral area 

 highly arched in the dorsal region and slightly carinated, projecting 

 over the oblong or round vent, which is placed at a considerable 

 elevation, usually about half-way up the total height. Dorsal 

 portions of the ambulacra quite plane ; in some examples the lower 

 part of the anteal or odd ambulacrum is slightly excavated. Plates 

 of the ambulacra large and broad, each equalling as much or rather 

 more than half the height of an interambulacral plate. In a rather 

 large example of this species there a.re 17 dorsal plates in each 

 [iv. viii.] 4 I 



