380 Professor Edwards Forbes on the Asteriadce 



fie, of the existing star-fislies having been lately extensively investi- 

 gated, and a good basis for comparison attained, it is time to inquire 

 into the history and generic relations of their fossil allies ; the more 

 so, as notices of not a few species are scattered through geological 

 memoirs. Numerous undescribed species exist in collections, and 

 good specimens of many recorded forms, of which slight fragments 

 only have been described or figured. The inquiry is one of great 

 interest ; for through it we may hope to attain a knowledge of the 

 earliest features of this important section of radiated animals ; to as- 

 certain whether the order, as a whole, has undergone material changes 

 durincf its progression in time ; whether the earlier forms were rudi- 

 mentary or equal in perfection of organization with those now living ; 

 and whether we can obtain information respecting the conditions of 

 climate or depth under which they lived in the several geological 

 epochs. The last point is especially important ; for as we know that 

 the forms of existing Echinodermata have a distribution highly cha- 

 racteristic of regions and conditions in space, we may hope to find an 

 analogical distribution of the fossil species in time. Whilst a great 

 part of the extinct zoophyte closely approximate existing types, a 

 larsre proportion even of the palaeozoic species bearing no small re- 

 semblance to existing forms the majority of the higher Radiata 

 which have been preserved exhibit generic, and even sectional differ- 

 ences, separating them from their living allies. These differences 

 are especially conspicuous among the Echinidre and Crinoidese. The 

 older genera, and even tribes of the last-named group, became ex- 

 tinct before the epoch of the secondary rocks commenced ; and in ex- 

 isting seas there are but few members of the crinoidal type. The 

 group is essentially chronomorphic. The Echinidse are doubtfully 

 indicated as yet among palaeozoic forms ; but those of secondary for- 

 mations frequently belong to genera which have become extinct, and 

 the development of which had an evident relation to points in time ; 

 for we find groupes of species, presenting peculiar combinations ot 

 characters, limited entirely to a few consecutive formations. This 

 centralization of a number of generic types in time among the Echi- 

 nidaj, whilst the members of others range indifferently through vast 

 epochs, is exactly analogous to the present distribution of sea-urchins, 

 many of the genera of which are confined to limited zoological pro- 

 vinces, whilst the members of others are distributed all over the 

 world. 



The knowledge of these facts, and an erroneous and too hasty in- 

 terpretation of them, led palaeontologists to believe that the distribu- 

 tion of the star-fishes in time was very limited, and had relation only 

 to recent epochs. They were supposed to have been entirely absent 

 during the palaeozoic epoch, an absence which, if true, would have 

 formed one among the many remarkable negative characters which 

 it apparently presents ; but which, it seems to me, have been laid 

 far too much stress upon, when we consider the slight acquaintance 



