. V. PRINCIPLES OF 



HELMINTHOLITHUS various, ac- 

 cording to the genus of the originals e. g. 



In reliquia of Pennatulas the fins (pinnce ) 

 connected with the midrib (racliis). 



Stylastra the united joints 



of the stipe (stipes}. 

 Asteriaj the whole of the 



crust or coriaceous covering of the 



hody. 



Echini the crust or calca- 



reous covering of the body, 



CONCHYLIOLITHUS various. C. g. 



In reliquia of Bivalves and Multivalves, 

 the united -valves. 



of adopting these parts, for the foundation of permanent species, 

 will readily be allowed, particularly as they afford sufficient spe- 

 cific differences, especially the dorsal scuta, formed by the anchy- 

 losed ribs and vertebrae, in Testudo. In the next genus of reli- 

 quia, Ichthyolithus, the necessity of taking so many parts, as 

 those above enumerated, for the distinction of permanent species, 

 will not perhaps be apparent In Fish, however, the relative 

 situation of the fins is a prime note of distinction in the Linnean 

 Orders, while the structure of certain parts of the head and the 

 form of the body generally characterise the genera These parts, 

 therefore, are neceSsary to determine the order and genus of the 

 prototype of an Ichthyohthus, according to the Linnean arrange- 

 ment ; and as specimens not unfrequently occur in which they are 

 all visible, we have taken such examples as standards of perma- 

 nent species, rather than those which exhibit only the more de- 

 tached parts of their originals. In the succeeding genera, Ento- 

 molithns, Ildmintholithus, Conchy liolithus, and Erismatolithus, 



