25 
taken from one of Knorr’s plates, Monumens des Catastrophes, Tome 
II. Tab. e. in. Fig. 3, is too imperfect to give a correct knowledge 
of its characters. 
The fossil, Plate II. Fig. 2, is, I believe, of this species, and has 
hardly suffered the least injury. It formed a part of Mr. Forster’s 
collection ; and is, I conjecture, from Oxfordshire. It needs no other 
notice of its form, than that it is nearly circular, deviating only in 
having that part of the shell, which is the region of the anus, a little 
more produced. It not having been thought necessary to figure the 
inferior surface, it is proper to observe, that it is slightly concave, 
the mouth being pentagonal, and the vent oval and transverse, and 
situated near the margin; but more on the under side, than it 
appears in the figure. 
The echini of the fourth section, Catocysti, are named Placentce, 
b) Klein, the shells being flat, like a cake, and variously formed 
They are all ornamented with a pentaphylloidal flower. The mouth 
is in the middle of the base, and the anus near to the margin, or to 
the third region of the axis. This section is divided by Klein into 
three genera, mellita, laganum, and rotula, which are comprised by 
Feske in the genus Echinodiscus, so named by Breynius. The 
charaeters of this genus are, a depressed, discoidal figure, nearly flat 
on both sides ; ambulacra imitating the forms of petals ; a smooth 
central mouth with teeth; the top perforated with four large pores. 
ie Mellita, honey-cake of Klein, forms the first family of this 
& enus. ie species differ in the number of foramina, the situation 
and the form of the periphery. 
Echinodiscus Imperforatus, B. quinquiesperforatus, B semes 
perforatus, E. emargmatus, E. auritus, E. immritus, B nuater- 
perforatus, do not appear to have been hitherto known in a petrified 
state The fossil which is represented Plate II. Fig. 8 is ? he onlv 
fossd winch I have seen of this family, and is undoubted^ one of the 
h species, Echmodiscm bisperforalus, as will appear, on a com- 
VOL, III, 
E 
