218 rUZZLES IN rAL^ONTOLOGY. 



the Vertebrata ! In the words of Heilprinn, " Most of the greater 

 divisions are already represented in the Cambrian, and, moreover, 

 are to be found in the lowest or oldest deposit — protozoons, 

 coelenterates, echinoderms, worms, articulates, and molluscs. 

 Moreover, some of these groups are already represented by a full, 

 or nearly full, complement of the orders assigned to them by 

 naturalists. Thus, the Cambrian echinoderms are represented by 

 forms belonging to three out of the six usually recognised orders, 

 viz.- — the Cysiidea, Crinoidea (ocean-lilies), and Asteroidea (star- 

 fishes). The last two have representatives living at the present 

 day," and form the highest development of their order. The 

 Crinoidea attained their highest development in the seas of the 

 Paleozoic period — Silurian, Devonian, and Carboniferous, and 

 have since then been pretty steadily declining. They are now 

 represented by not more than half-a-dozen generic species. The 

 Asteroidea, on the other hand, have just as steadily been increas- 

 ing, and, indeed, attain their maximum development in modern 

 seas. Heilprinn states that " A star-fish has lately been dredged 

 up by the Travaillenr expedition from depths of 1,960 and 2,650 

 metres, having on the dorsal surface a true peduncle, apparently 

 absolutely homologous with the stalk of a crinoid." Also, in some 

 fixed crinoids, tlie " tuft" separates from the column after a certain 

 period of existence, and then leads an independent life {Coi/ia- 

 tula). One might naturally suppose that the free was a later 

 development than the fixed form, yet both Crinoidea and Asteroi- 

 dea are found perfectly distinct in the oldest fossiliferous strata. 

 'I'hc Cambrian MoUusca comprise representatives of no less than 

 'iw^ of the six classes which now inliabit tlie seas, namely — the 

 Brac/iiopoda, AcepJiala, Ftenpoda, Gasteropoda, and Cephalopoda. 

 Here, again, we have api)arL'ntly a simultaneous appearance of 

 lower and higher forms. 



A few types of Brachiopods have survived to the present day. 

 Thus, the Lingnla, of the Cambrian rocks, is very little, if at all, 

 different from the existing Liugula, though millions of years have 

 elapsed since this mollusc first appeared, and higher types innu- 

 merable have run tht-ir short race and vanished. 



In the Ui)per Cambrian, we find Molluscan forms belonging 

 tu the highest order — the Cephalopoda — but not to the highest type 



