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vol,. 79 



not possess a carapace, and as a result of a wrong determination 

 of an unmovable head spine as " antennule " the appendages of the 

 head have been misunderstood. The only character it has in com- 

 mon with the trilobites is that all segments of the trunk bear legs. 

 All other characters, among them the possession of A2, oppose its 

 reference to the trilobites and point rather to the Notostraca (with 

 exception of the strong development of A2, the division of the legs, 

 the absence of a carapace). Fedotov's suggestion of the relationship 

 of Marrella with Conchostraca and Cladocera is nullified by such 

 characters as the flat, free head, the widely separated eyes, and other 

 features. If Walcott considered Mairella more highly developed 

 than Apus^ he reversed the facts, since the lack of division of the 

 legs of Apus is a later development. (Fig. 3.) There is nothing 

 similar to it among the trilobites, especially now that Barrande's 

 figure of Bohemilla^ which could perhaps have been quoted, has been 



corrected by Kloucek. Mar- 

 7'ella is therefore a primitive 

 branchiopod of still simpler 

 structure than the Notostraca 

 [Richter]. 



This brief survey shows that 

 Marrella has thus far remained 

 a very fractious puzzle and 

 that any additional knowledge 

 concerning it would be most 

 vrelcome. In fact, a study of 

 the large quantity of material 

 now made available, with the 

 new ultra-violet light method, is most desirable. For, as we shall 

 see presently, here is a Cambrian trilobite freslily molted and exhib- 

 iting all its body anatomy ! 



In the small suite of slabs containing the problematic fossils from 

 the Burgess shale, suggestive of graptolites, was one bearing several 

 specimens of Marrella splendens. Wlien these, with the supposed 

 neighboring graptolite, were brought under the Lapworth-Parkes 

 microscope, not only the amazing delicacy of the body but also the 

 distinct identity of the appendages with those of a trilobite became 

 apparent. Likewise the absence of any protecting carapace was too 

 evident to be overlooked. All these observations point toward the 

 fact that the fossil may represent a freshly molted trilobite. Fol- 

 lowing up this clew, the writer recalled having previously read of 

 such a suggestion, and a search of the literature revealed that Edgar 

 Dacque, in his brilliant Vergleichende biologische Formenkunde der 

 fossilen niederen Tiere (1923, p. 703), incidental to the discussion 

 of the fact that many trilobite carapaces, especially when heaped 



Figure 8. — Early growth stage of Apus: 1, 2, 

 3, Cephalic appendages; I, II, III, IV, V, 

 body sogmonts. (From Lang's Comparative 

 Anatomy) 



