18G On Cyrtoma, a new genus of Fossil Echinida. 



I have named this species in compliment to Sir J. F. 

 Herschel, for the interest expressed by that philosopher 

 in the further investigation of the subject of these fos- 

 sils. 



2. Cyrtoma prinsepiana. J. M. t. vi. figs. 1. 2. 3. 



Apex symmetrical, and equal in altitude to about half the 

 shortest diameter of the disc. Petaloid star surrounding the 

 apex, and the clavate star surrounding the mouth, each limb ter- 

 minating in double rows of large ambulacral pores, which are 

 continuous across a narrow rounded disc. 



I name this species in compliment to James Prinsep, Esq., 

 Secretary to the Asiatic Society of Bengal, whose departure 

 from India in consequence of sudden and melancholy illness, 

 is here felt as a public loss by all classes interested in the 

 advancement of science. 



3. Cyrtoma Griffiths, J. M. t. v. figs. 4. 5. 6. 



Apex symmetrical, equal in altitude to half the diameter, and 

 surrounded by a petaloid rosette ; ambulacra each composed of 

 two rows of long transverse holes. Inferior ambulacra pro- 

 minent and narrow. Disc thin and sharp. With large anambulac- 

 ral plates on the lower surface. 



This species is named in compliment to William Griffith, 

 Esq., to whose subsequent visit to the Khasyah mountains 

 I am indebted for it. 



4. Cyrtoma dentata, J. M. t. vi. figs. 4. 5. 6. 



Apex anterior to the middle, and equal in altitude to half 

 the short diameter ; anal ridge low and obscure ; upper rosette 

 flat ; pores oblong, transverse and very close. Lower surface, con- 

 cave ; anal denticulations prominent. 



Cystoma duracina, J. M. t. vi. figs. 7. 8. 9. 



Apex anterior to the middle, and equal in altitude to half the 

 long diameter ; below fiat ; ambulacra and anambulacra raised 

 on the edges and rough. Inferior rosette consists of sharp ridges 

 without pores. 



5. Cyrtoma depressa, J. M. t. v. figs. 7. 8. 9. 



Disc nearly round, apex anterior to the middle, and scarcely 



