27 



composed of a line formed of single pores, surrounded by three, four, 

 five, or even six lines, of minuter pores, obliquely disposed in very small 

 grooves. What figure resulted from their approximation in the centre 

 cannot be determined, as the shell is in that part broken. 



On examining the surface of this fossil with a lens, it was found still to 

 retain, in several parts, the small flat imbricating spines. These are 

 represented in the sketch on the right side of the fossil. 



Echinodiscus reticulatus is not known fossil. E. Orbicularis, Tab. XLV. 

 Fig. 6, 7 ; Lang. Tab. xxxv. Fig. ulthn. ; is a depressed orbicular echi- 

 nite, about an inch in diameter, with acute oval ambulacra, and ten 

 porous rays in the base ; the mouth round and the anus small, and mid- 

 way between the centre and the margin. E. Rosaceus, Tab. XL. 4, Lesk. 

 et Tab. E, in. 8, Knorr. differs from the former, in being much smaller, 

 and in its ambulacra forming a floweret, with very short petals, round 

 the vertex. 



Echinodiscus decies digitatus, octodigitatus et dentatus, do not ap- 

 pear to be known as fossils. 



Under the class Catocystus a new genus has been formed, by Phel- 

 sum, and named Echinocyamus. The generic characters are, ten stel- 

 lated ambulacra, passing from the top in straight biporous rows'; the 

 mouth and anus adjoining in the middle part of the base. The shells of 

 this genus are not known in a petrified state. 



