REPORT ON THE ECHINOIDEA. 25 



with but slight modifications to the present day, or at the same time may become 

 modified in endless ways, and form the innumerable combinations with other structural 

 features which have given to the Echinid fauna of any period or to that of the present 

 day its typical features. 



Connection between the Cretaceous and the Recent Echinid Faun^. 



One of the ver}^ first results clearly indicated by the deep di-edgings of Count Pourtalfes, 

 and the subsequent investigations of the "Porcupine" expedition, was the antique character 

 preserved by many of the new genera discovered in deep water, and especially their resem- 

 blance to Cretaceous genera ; and the study of the Challenger Echinids has brought this 

 out stUl more plainly. 



For the purpose of making the comjiarison of the Challenger Echinids with the earlier 

 Cretaceous types as comjjlete as possible, it will be interesting to take a rapid review of 

 the Cretaceous Echinid fauna, and contrast it with the abyssal fauna taken as a whole, 

 independently of its combinations in time with the littoral and continental types, but 

 not independently of its combination with those types which extend into the abyssal 

 fauna either from the littoral or from the continental fauna. 



On comparing the genera characteristic of the Chalk with those now found li-\ang, we 

 find that a considerable number of the latter date back to the Cretaceous period ; and a few 

 of the Cidaridse, the Echinidse, the Salenidse, the Echinoconidse, and the Petalosticha, even 

 to earlier epochs, to the Jurassic beds, the Lias, and the Trias. The genera Dorocidaris, 

 Phyllacanthus, Forocidaris, Salenia, Podocidaris [Magnosia, Codiopsis), Asthenosoma, 

 Phormosoma {Echinothuria), Temnechinus, Cottaldia, Phymosoma, Holopneustes, Hemi- 

 pedina, Echimis, Echinocyamus, Fihularia, Echinolampas, Rhynchopygus, Conoclypus 

 (J.), Echinobrissus, Catopygus, Pygaster, Pourtalesia [In/ulaster) , Hemiaster, Periaster, 

 are in this category, so that a good proportion of the genera of Echinids still living in 

 the present epoch belong to genera already existing at the time of the earliest Cretaceous 

 formations ; and leaving out for the present the genera which have disappeared during 

 Tertiary times, we find in the Tertiaries, in addition to the above genera, the following 

 which have continued to the present time : — Arhacia, Ccelopleurus, Echinometra, 

 Stomopneustes, Strongylocentrotus, SpJuerechinus, Temnop>leurus, Trigonocidaris, Sal- 

 macis, Amhlypneustes, Toxopneustes, Hipponoe, Clypeaster, Echinanihus, Laganum, 

 Echinarachnms, Arachnoides, Echinodiscus, Mellita, Encope, Echinoneus, Nucleolites, 

 Homolampas, Paleopneustes, Spatangus, Maretia, Eupatagus, Lovenia, Breynia, Echi- 

 nocardium, Brissopsis, Agassizia, Brissus, Metalia, Meoma, Linthia, Schizaster, Moira. 



Leaving as genera belonging strictly to the present epoch, which for tlie present we 

 may take as the result of the existing condition of things, and as the successors of 



(ZOOL. CHALl. EXP. — PART IX. 1881.) I 4 



