BRITISH FOSSILS. 



DECADE THE THIRD. 



The third Decade of representations of British Fossils follows up the 

 subject of the first, and continues the series of illustrations of the 

 genera and species of extinct Echinodermata, especially those belonging 

 to the orders Asteriadce and Echinidce. 



The genera illustrated in this Decade are partly new, partly long- 

 established ; so also with the species, some of the most remarkable of un- 

 published forms having been selected, as well as some of the commonest 

 and best known fossils. Yet, even respecting those which are so familiar 

 that their whole history is believed to have been long ago made out, 

 there is so much to be cleared up, so many points of structure hitherto 

 very imperfectly or not at all elucidated, and such an accumulation of 

 synonyms, that their investigation is much more laborious, and occupies 

 much longer time, than inquiries into entirely new types. Thus, three of 

 the fossils figured and described in this Decade, Hemicidaris interme- 

 dia, Galerites albogalerus, and Micraster cor-anguinum, are so familiar 

 to geologists and naturalists, so abundant and so well preserved, that 

 authors do not hesitate to cite them without comment, as if they were 

 free from any obscurity. Nevertheless, I may say confidently, that 

 not until now has the literature of these well-known and often-described 

 forms been cleared up, and many of the most important points in their 

 organization made known. Common as they are, no representations of 

 them, presenting sufficient details of their structure, have ever appeared 

 before. 



Among the new forms now first described and figured, some are of 

 singular interest. Two of them, the Lepidaster Grayii and the Tropi- 

 daster pectinatus, are not only new as species, but unquestionably possess 

 features entitling them to become the types of new genera. Of those 



b 



