. DE ECHINIS. 197 



but others with a flatter surface may be compared to a shield ; hence they are termed 

 Echini clypeati. 



The Brissus (Bpfo-trog) is enumerated by Aristotle in his fifth book of the ' History 

 of Animals ' as the tJiird genus of Echini. But since his translators have not sanctioned 

 what this naturalist understood by that term, I have applied the name of Brissus to this 

 genus. 



No recent Echinobrissus has come under my observation, but I have seen some fossil 

 species, although these latter are by no means common. Morton assigns only one aperture 

 to this Echinus, since the other situated in the furrow escaped his notice ; but Woodward 

 ought afterwards to have discovered it, since he enumerates it among the Echini which 

 have two apertures, the other being in the furrow. 



Table VI, fig. 1. The Echinobrissus planior or Clypeatus minimusj fossil; filled 

 with stony matter ; with the anal aperture in the furrow. From England. [Echino- 

 brissus clunicularis.'\ 



Fig. 2. The base with the oral aperture. 



Fig. 3. Echinobrissus ELATIOR ; more or less raised ; fossil; filled with stony matter. 

 From England. [Echinobrissus scutatus, a characteristic fossil of the Coralline Oolite.] 



[Plate LVI, figs. 1 and 2 represent several type forms of Echinobrissi from the Creta- 

 ceous formations. This genus has one living representative species.] 



Genus VII. — The Echinodiscus is an Echinus with the oral aperture situated near the 

 centre, but ivith the anal between the centre and the margin or on the margin. 

 The form always somewhat flattened. 



All the species of this genus have the likeness of a five-leaved flower upon the upper 

 surface. 



I have termed it Echinodiscus from the figure of a disc or orb. 



As I have not seen any recent Echinus of the genus iumiediately preceding, so, on the 

 other hand, I have never hitherto observed a fossil of this genus. The foUowing species 

 were all brought from the Eastern Ocean. 



Table VII, fig. 1. The Echinodiscus circinatus minor, with the margin entire. 



Fig. 2. The base or lower portion, in which is seen the anal aperture, but the other 

 (the oral) in the middle is not visible on account of the mutilation of the shell in the 

 centre. 



Fig. 3. Echinodiscus, one half of the circumference generally marked with equal 

 indentations. 



Fig. 4. The base, in which are seen the oral and anal apertures." 



