igi6. No. lO. THE LOWER CAMBRIAN HOLMIA FAUNA. 93 



On the other hand, he contends that we find such transition forms in the 

 genera Redlichia and O/enopsis, whilst Albertella and Zacanthoides repre- 

 sent further stages of development of Mesonacidae. 



As regards the first, Walcott sa\*s in his work that we quoted 

 previously: "In the western Pacific Province fauna of China, India and 

 Australia, the genus Redlichia appears to be a form that combines charac- 

 teristics of both families"^. In a later work he says: ''Redlichia is an 

 intermediate form that serves in a limited degree to connect the Mesotia- 

 cidae and the Paradoxidae. The tapering glabella and elongated eye-lobes 

 recall those of Xevadia, and its small pygidium that of Ho/fnia a.nd Callavia" '-. 



We must first of all observe that Redlichia even in China is found 

 in a typical Lower Cambrian fauna, i. e. at a much older stage in the 

 series than might be expected of a "missing link" between the two families. 

 On the contrar}', the structure of the glabella is found to be far more 

 primitive than that of the genera of Mesonacidae in the upper part of the 

 Lower Cambrian from which Walcott derives Paradoxidae!" As the facial 

 suture is open, it would appear to be more natural to regard this genus 

 as a special line of evolution, that even at an early stage developed from 

 the same main stock as was the case with Mcsouacidae and Patadoxidae, 

 and which has retained several primitive features in common with the 

 latter forms. 



Regarding the Sardinian genus Oleuopsis, which Walcott rediscovered 

 in North America and which appears here at the uppermost part of the 

 Lower Cambrian and in the transition beds to the Middle Cambrian, Wal- 

 cott says^: "Dr. J. F. Pompecki considered it probable that Oleuopsis 

 was derived from Paradoxides, but with our -present information I am 

 inclined to consider that Oleuopsis is more likely to be a form intermediate 

 between Holmia (restricted) and Paradoxides, or that the two genera are 

 descendent from the Holmia type of the Mesonacidae". 



For the same reasons as in the case of Redlichia — i. e. the primi- 

 tive structure of the cranidium — both the above assumptions appear to 

 be ver\- improbable. I believe that Matthew^ was far more correct in 

 comparing this genus with Protoleuns. In my opinion it can natural!}' be 

 regarded as a flat bottom form, that at an early period developed from 



1 Olenellus and other genera of Mesonacidae, 1910, page 254. 



- The Cambrian faunas of Eastern Asia, 19 14. page 60. (Smithsonian Misc. Coll. Vol. 



64. No. II 



See also : Ch. Walcott. "The Cambrian Faunas of China", 1913. 

 ^ The Sardinian Cambrian genus Oleuopsis in America, 1912, page 239. (Smithson. Misc. 



Coll. Vol. 57. No. 8 » 

 -♦ Ch. Walcott, Cambrian Trilobites, 1908. 1 Smiths. Misc. Coll., vol. 53, No. 2). 



