PROM THE WHITE CHALK. 275 



His figures are very poor, and the varieties which he has united under the name appear to 

 comprise forms which do not properly belong to the type. Goldfuss was the first who, in 

 1829, gave an exact representation of the test from the able and accurate crayon of Herr 

 Hohe. He separated it from his Spatangus cor-testudinarium, with which it had been 

 united ; but the authors who followed Goldfuss have forgotten the distinction pointed out by 

 him ; thus Agassiz and Desor in 1847 reunited these two species, and considered Micraster 

 cor-testudinarium only as a large variety of Micraster cor-anguinum. Forbes in 1850, and 

 d'Orbigny in 1853, increased the confusion, for by them nearly all the species of the 

 White Chalk were referred to one and the same type, and Micraster gibbus, rostratus, 

 cordatus, cor-testudinarium, latus, armatus, brevis, &c, successively established by different 

 authors, were only admitted as simple varieties of Micraster cor-anguinum. 



Professor Hebert after a careful study and comparison of the species of Micraster 

 reunited by Porbes and d'Orbigny, arrived at an opposite determination ; not only did 

 he admit the validity of Micraster cor-testudinarium, gibbus, and brevis, but he determined 

 two other species. The structure of the ambulacral plates is the principal character 

 upon which M. Hebert founds the description of his species. 



In his ' Synopsis des Echinides Possiles,' published since Professor Hebert's memoir, 1 

 M. Desor persists in uniting Micraster cor-testudinarium to M. cor-anguinum, and admits 

 under reserve M. Brongniarti, Heb., and M. Desori, Heb., proposed therein with such 

 diverse opinions about the true characters of this old fossil. When M. Cotteau was about to 

 describe the species in his classical work on the ' Echinides du departement de la Sarthe,' 

 he determined to study the species anew, and for this purpose collected all the necessary 

 documents for reference and numerous specimens for comparison, and says, " Without 

 adopting entirely the conclusions of M. Hebert we believe, nevertheless, that there exists 

 among the Micrasters which d'Orbigny has confounded under the same denomination four 

 species very distinct, viz." 



" 1st. The Micraster cor-testudinarium, Goldfuss," admirably figured and described 

 by Cotteau. 



"2nd. Micraster gibb us, Agass. Spatangus gibbus, Lam." (Epiaster gibbus of this 

 work.) " Well represented in the ' Atlas de l'Encyclopedie Methodique,' pi. clvi,figs. 4 — 6, 

 and remarkable for its elevated conical form, its long straight ambulacra, its large, flat 

 under surfaces, truncated posterior border, with its vent placed low down near the angle." 

 Remarkable also, I may add, for the want of the subanal fasciole, which has been over- 

 looked by Porbes, d'Orbigny, and Cotteau : so that assuming the presence, absence, or 

 character or number of the fascioles to afford characters for generic division, this species 

 would not belong to the Micrasters at all. 



" 3rd. The Micraster Brongniarti, Hebert, figured for the first time by Brongniart 

 in his ' Possils from the Environs of Paris ' under the name Micraster cor-anguinum, and 



i < 



Etude sur les Terr, cretaces, Mem. Soc. Geol. de France,' 2e serie, torn, v, pi. xxix, fig. 19. 



