10 ECHINODERMS OF THE CRAG. 



The species of this genus are all small, and difficult to distinguish. Almost all arc 

 tertiary. A few are found existing. 



1. EcHiNOCYAMUs PUSiLLUs. Plate I, figs. 8 — 15. 



Spatangus PUSILLUS, MuUer. Zool. Dan., p. 18, tab. xci, figs. 5, C. 



Echinus minutus, Gmelin. Linn., p. 3194. 



EcniNOCYAMUS minutus. Be Blainville. Man. d'Actin., p. 214. 



— ANGULOsus, Leske ap. Klein., p. 215. 



— — Agassiz. Mon. des Scutelles, p. 130, tab. sxvii, figs. 17, 18. 

 EcHiNOCYAMUS ANGULOSUS, Agassiz and Desor. Ann. Sc. Nat., 3d series, torn, vii, 



p. 140. 



— — Duben &nA Koren. Kong. Vet. Akad. Hand., 1844, p. 279- 

 FiBULARiA ANGULOSA, Be Blainville. Diet. Sc. Nat., torn, svi, p. 512. 



— — Lamarck. An. sans Vert., vol. iii, p. 17. 



— — Besmoulins. Tab. Syn., p. 236. 

 EcHiNOCYAMUS PUSILLUS, Fleming. Brit. Anim., p. 481. 



— — Forbes. Brit. Starfishes, &c., p. 175, (fig.) 



— — Agassiz. Mou. dcs Scutelles, p. 128, tab. xxvii, figs. 1 — S. 

 FiBULARiA TARENTINA, Lamarck. 



EcHiNOCYAMUS TABENTINUS, Agassiz and Besor. Ann. Sc. Nat., 3d series, torn, vii, 



p. 140. 



This very common, widely distributed, and very variable little urchin, is an abundant 

 fossil in the Red Crag, especially at Alderton, Suffolk, assuming numerous changes of 

 form, all however distinguished with facility by the position of the anus half way, or 

 nearly so, between the mouth and tlie posterior margin, and by the coarse and rather 

 conspicuous tubercles of the surface. The avenues of pores are sub-parallel, and slightly 

 radiating. The margin is always more or less tumid, and sometimes almost swollen. 

 The mouth is large, round, and conspicuous. The vent is also large. The exterior 

 is strengthened by strong buttresses. In the living state, the test is covered with 

 thick-set minute squaniatcd spines, turning of a powdeiy-grecn colour, as the animal dies. 



The principal varieties, all of which, however, pass into each other, are the fol- 

 lowing : — 



a. JVormalis, regularly oval, and tumid, (PI. 1, tigs. 8 — 13.) 



6. Botundus, nearly orbicular, and tumid, (PI. I, fig. 15.) 



c. Depressus, rounded or ovate, much compressed above. 



d. Ariffulosus, approaching an ovato-pentagonal shape, (PL I, fig. 11.) 



e. Triangularis, sub-triangular, and sometimes curved, (PI. I, fig. 10.) 

 /. Tumidus, ovate, and much swollen. 



The last two forms are rare. All variations of shape between nearly completely circular, 

 and narrowly ovate, nmy be taken in the one locality at the present day. A rather large 



