21 



which is subuculus, and is only known as a fossil. The surface of this 

 is divided in the same way as the former species. The periphery is cir- 

 cular. The vertex is much more depressed, and the base rather more 

 concave. One of this species is represented Plate II. Fig. 7. 



Another genus is here introduced by Phelsum, and named by him 

 Echinoneus. It agrees, in every respect, with E. Discoides of Linnaeus, 

 except in its periphery, which is rather ovate, and not angular. It has 

 the same number of areas and ambulacra; the latter being biporous, and 

 having the pores more distant from each other than in the preceding 

 genus. 



The second section of the class of CATOCYSTI is Cassis (helmet-stone.) 

 These echinites are distinguished by an oval base, from which the shell 

 rises in a vaulted helmet-like form. One extremity of the oval, that in 

 which the vent is placed, is commonly more produced and acute than 

 the other. Klein divided these echinites according to their size, into 

 two genera, galea and galeolte ; but Leske, considering the difference of 

 size as not sufficient to affect the genus, has very properly included 

 them both under the genus echinocorys. As the echini of this extensive 

 genus are only found fossil, the changes which they have sustained' from 

 various kinds of injuries, prevent, in many instances, their species being 

 exactly determined. 



The first species, .Ecliinocorys 'scutatus, Tab. xv. A. B. Kldnii, is in 

 general as high as it is long. It has, like most others, five large and 

 five small arese, separated by biporous ambulacra. Minute tubercula 

 and granulse exist on some parts of the surface, and particularly on the 

 base and near to the mouth. The base, the circumference of which is 

 nearly elliptical, is almost flat : the edge, however, is slightly rounded ; 

 and, in its middle, a prominent slip extends from the mouth to the anus, 

 near to which, on each side, two bands of minute granulae are disposed. 

 The mouth is reniform, placed crossways, at the broadest extremity. 

 The anus is of a roundish oval figure, and is near to the narrow extre- 



