60 
Trias sic Echinoderms ot Bakony. 
A. Gras, Descr. des oursins foss. du Dept. de l’Isere. Bull. Soc. stat. Isere, IV, p. 
289 and p. 444; 1848. 
T. Wright, Monograph on the Brit. foss. Echinodermata of the Oolitic formations. 
Part I. London, Palaontogr. Soc.; 1857. 
E. Desor, Synopsis des Echinides fossiles, pp. X—XIII; 1858. 
A. Agassiz, Revision of the Echini, Part IV. Illustr. Catal. Mus. Comp. Zool. 
Harvard; 1874. 
S. Loven, Etudes sur les Echinoi'dees. Svensk. Vet.-Akad. Handl. (n. s.) XI, No. 7; 1875. 
P. M. Duncan, Revision of the . . . Echinoidea. J. Linn. Soc., Zool., XXIII; 1889. 
See pp. 295 — 304. 
The terminology of the last-mentioned author is followed so far as possible; 
but, since every increase in precision of description demands the revision of accepted 
terms or the addition of new ones, it may save ambiguity if attention be here 
drawn to a few of those frequently used in this memoir. 
The Test of a Regular Echinoid in the normal position has an upper a p i c a 1 pole 
and a lower oral pole. With reference to these poles, the regions of the test or of its 
adapical 
inter- yf. ad- per¬ 
radial radial radial 
oblique suture suture suture suture 
t 
adoral 
Text-fig. 6. Geneneral Orientation of Echinoid ambu- 
lacra and interambulacra. 
adapical 
Text-fig. 7. The normal direction of imbrication 
in Echinoid ambulacrals and interambulacrals is 
shown by the arrows. 
components are adapical or adoral. There is no need for such terms as dorsal, ventral, 
abactinal, actinal, which generally breed confusion. 
We deal here only with the Corona, i. e. the test minus the apical System and 
plates of the peristomial and periproctal membranes. The corona is composed of ambu- 
1 a c r a (strictly these should be called ambulacral areas) and interambulacra. These 
meet along the «ambulacro-interradial vertical sutures» (Duncan) here termed ad radial 
suture s. (Text-fig. 6.) 
Each Interambulacrum consists of plates, called interambulacrals, which, in 
the genera hereinafter discussed, except those of the Tiarechinidae, are arranged in two 
vertical c o 1 u m n s, meeting in a zigzag suture, the interradial suture; and each 
Ambulacrum consists of two columns of ambulacrals meeting in the p e r r a d i a 1 
suture. In questions of Orientation the numbering of Loven (1875, pp. 13, 14, 20 et 
sqq.) is used whenever possible. In accordance therewith, in any isolated ambulacrum or 
interambulacrum, as viewed from the exterior with the adapical end uppermost, the column 
