96 Dr. T. Wright on the Cassidulidse of the Oolites. 



sphcericus in its general outline, but is well distinguished from it 

 by the position of the anal opening. In H. depressus the anus 

 is infra- marginal with the apex directed inwards, whilst in H. he- 

 misphcericus that opening is marginal with the apex directed out- 

 wards. The specimens from the Inferior Oolite are in general 

 smaller and more tumid than those obtained from the Cornbrash, 

 which have a much greater diameter, but are proportionally more 

 depressed and have a more acute basal angle. 



Locality and stratigraphical range. — I have collected this Ur- 

 chin from the upper beds of the Inferior Oolite along the entire 

 range of the Cotteswolds. Dundry, Wootton-under-Edge, Stinch- 

 combe, Rodborough, Coopers, Birdlip, Shurdington, Leckhamp- 

 ton and Winchcombe Hills may be named as good localities in 

 Gloucestershire. I have obtained the large specimens from the 

 Cornbrash near Kemble Tunnel, Great Western Railway, and 

 from Stanton, Wilts, and near Woodstock, Oxon. Mr. Phillips has 

 found it in the Cornbrash of Yorkshire. The foreign localities 

 are, "the corallian stage of Liesberg, environs of Bamberg, 

 Muttenz, Metz, the Oxfordian stage of Vivoin and Chauffour 

 (Sarthe), d'Alenyon, Boulogne, Mamers, Chatillon-sur-Seine and 

 Latrecy (Haute Marne) *.^' Goldfuss assigns as its localities 

 the up})er and middle beds of the Jurakalk in Bavaria and WUr- 

 temberg f. Koch and Dunker have found it in the sandy 

 dolomitic limestone of Tonnjesberges in Hanover %. 



History. — Holectypus depressus has been long known to palae- 

 ontologists, being very generally found in the lower and middle 

 divisions of the Jurassic strata throughout Europe ; it is figured 

 in the works of Goldfuss, Koch and Dunker, and Agassiz : the 

 figures of the latter author are the most correct and abundant in 

 details. usi 



Holectypus hemisphcmicus, DesoY. :• 



Syn. Discoidea hemisphisrica, Agassiz, Cat. Syst. p. 7; Desori ' 



Monogr. des Galerites, p. 71. pi. 8. fig. 4-7. '*' 



Holectypus hemispharicus, Agass. and Desor, Cat. raisonn^ des Echi-; 



nides, A. S. N. vol. vii. p. 146, 3rd Series. >? 



Galerites hemisphcBricus, Forbes, Memoirs of the Geol. Survey, Dqt . 



cade 3. pi. 6. 

 Var. a. Depressus. — Discoidea maryinalis, M*Coy, Ann. Nat. Hist. 



vol. ii. p. 413, 2nd Series. 

 Var. b. ConicuSy anus valde marginalis. — Holectypus Devauxianus, 



Cotteau, Etudes sur les Echinides fossiles, p. 46. pi. 2. fig. 7-9. 



Test tumid, hemispherical, more or less depressed; margin rounded; 

 tubercles larger on the ventral than on the dorsal surface, and 

 increased in size around the mouth ; single interambulacrum 



* Ann. des Sc. nat. tome vii. p. 145, 3rd Series. 



t Petrefact. Gennaniae, Part 1. p. 130. tab. 41. 



X N. D. Oolith. Versteinerungen, p. 40. tab. 4. fig. 2. 



