lO SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I48 



of short spines. Calodiscus reticulatus has a strong reticulate orna- 

 mentation. 



Classification. — The Eodiscidae of North America have so far 

 been referred to five genera (Rasetti, 1952) : Calodisctis Howell, 

 1935 (type species, Agnostus lobatus Hall) ; Dawsonia Hartt in 

 Dawson, 1868 (type species, Microdiscus dawsoni Hartt in Dawson) ; 

 Eodiscus Hartt in Walcott, 1884 (type species, Eodiscus pulchellns 

 Hartt in Walcott^ Microdiscus scanicus Linnarsson) ; Serrodiscus R. 

 and E. Richter (type species, Eodiscus {Serrodiscus) serratus R. 

 and E. Richter) ; and Weymouthia Raymond, 1913 (type species, 

 Agnostus f nobilis Ford). Of these five North American Eodiscid 

 genera, Dawsonia and Eodiscus occur exclusively in the Middle Cam- 

 brian Paradoxides beds ; the other genera are Lower Cambrian. 



Genera that have been proposed for Eodiscidae from Europe 

 and Asia are Cobboldites Kobayashi, 1943 (type species, Microdis- 

 cus comleyensis Cobbold) ; Metadiscus Kobayashi, 1943 (type spe- 

 cies, Microdiscus sculptus Hicks) ; Ladadiscus Pokrovskaya, 1959 

 (type species, Ladadiscus limbatus Pokrovskaya). To these genera 

 the writer would add Tannudiscus Pokrovskaya, 1959 (type spe- 

 cies, Tannudiscus tannuolaicus Pokrovskaya), originally assigned to 

 the family Opsidiscidae (Pokrovskaya, 1959), which seems of 

 questionable validity since Opsidiscus, which has vestigial eyes but 

 no facial sutures, could be referred either to the Pagetiidae or the 

 Eodiscidae, the presence of a transglabellar furrow having little sig- 

 nificance. Tannudiscus has no trace of eyes and should be placed in 

 the Eodiscidae even if a separate family Opsidiscidae were recog- 

 nized. 



The nine new genera described herein approximately double the 

 size of the family and it was considered whether the additional 

 knowledge suggested some grouping of the genera that would indicate 

 evolutionary trends. On the basis of present knowledge there seems 

 to be no basis for a meaningful arrangement of the genera. The glabel- 

 lar lobation, which in general is one of the important taxonomic 

 features in trilobites, seems of little significance, as shown by the 

 gradual transition from generalized lobation to the specialized loba- 

 tion where all furrows have disappeared but for a deep, straight 

 transglabellar furrow (Calodiscus reticulatus) . Other characters, such 

 as shape and relative length of the glabella, cephalic border furrow 

 and border, glabellar, occipital and marginal cephalic spines, orna- 

 mentation, etc., seem even less significant, as also are believed to 

 be the pygidial features. Even an arrangement of the genera based 

 on characters of little evolutionary and taxonomic significance would 



