6o4 SCIENCE PROGRESS 



Raymond's considerable extension and revision of the fine 

 work done by Beecher and by Walcott has been supplemented 

 by a further publication on Neolenus by Walcott in 1921, and 

 its author, whose first paper on trilobites appeared nearly 

 forty years ago, now tells us that he proposes to reconsider these 

 organisms when he has set his ideas in order " in the course 

 of two or three years." Could anything represent more ade- 

 quately devotion to the trilobitic cult ? 



William Smith, when he laid down the principles of strati- 

 graphical geology in the west of England during the strenuous 

 Napoleonic years, urged that the succession of organic forms 

 entombed in rocks had been designed to help the miner and 

 the engineer. He would have been delighted to find how 

 the successive genera of trilobites assist the classification of 

 the most ancient fossiliferous rocks. The variety of structure 

 in Lower Cambrian genera is amazing. These forms must have 

 had ancestors, which were possibly soft all over and left no 

 carapaces behind, Beltina dani, a crustacean appendage from 

 pre-Cambrian strata in the Belt Series of Montana, has been 

 referred by Walcott to the eurypterida, an arachnid race far 

 higher then the trilobites, especially in the structure and locali- 

 sation of their limbs. From Cambrian times to the close of the 

 Gotlandian period trilobites can be employed as indicating 

 successive zones. Their relative position in the sequence 

 of strata in the field had to be first determined ; no purely 

 zoological inferences must be allowed to dominate discussion. 

 I have elsewhere related the somewhat humorous reversal 

 of opinions as to " primitive " characters in trilobite genera, 

 when the true position of the Olenellus-beds of North America 

 was established (" The Story of Olenellus," Natural Science, vol, 

 I, p. 340, 1892), The result of exploration was to give immense 

 importance to a genus previously obscure, and Olenellus and 

 its associates, the Olenellus-fauna, now mark the Lower Cam- 

 brian beds throughout the world. Anything below the Olen- 

 ellus-beds must be pre-Cambrian ; in Britain, the Longmynd 

 range of the Welsh border, once held to be Cambrian, and 

 the " Dalradian Series " of the Scottish highlands, long 

 regarded as Ordovician, have, through the occurrence of 

 Olenellus in overlying zones, been assigned to this dignified 

 antiquity. 



The Middle Cambrian has been marked in North America 

 by Olenoides and in Britain by Paradoxides, which is probably 

 the largest of the trilobites. The zone-trilobite of the American 

 Upper Cambrian is Dicellocephalus, a genus with a spade-like 

 expansion in front of the glabella, Dicellocephalus is also well 

 known in Europe ; but the typical Upper Cambrian tribolite 

 on this side of the Atlantic is Olenus. Enough has been said, 



