4 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 149 



commonly considered guides to either the Late Ordovician or the 

 Middle Ordovician, but not both, as well as other species known to 

 be common to both. Dating such a mixture of species becomes a 

 highly subjective matter because different criteria are invoked by 

 different paleontologists in interpreting the mixture. 



The association of Ptychopleurella, Dicoelosia, Diambonia, Ptycho- 

 glyptus, Christian™, and Cyclospira suggests close equivalence with 

 the fauna from Perce, Quebec, summarized and dated by Charles 

 Schuchert and described by G. A. Cooper (Schuchert and Cooper, 

 1930). Revisions and additions to the descriptions were made later 

 by Cooper and Kindle (1936). A review of the original paper by 

 Schuchert and Cooper shows that the Late Ordovician age was based 

 primarily on the occurrence of Dicoelosia. 



With the exception of that genus, all the other Perce forms, plus 

 Xenambonites and Anoptambonites, are reported from the Caradoc 

 of Girvan, Scotland, by Williams ( 1962) . It is Williams' conclusion 

 (pp. 57-62) that the Girvan Caradoc can be closely correlated with the 

 Middle Ordovician of eastern North America, equal to the Porterfield, 

 Wilderness, and Trenton Stages of Cooper (1956). 



Within the Alaskan assemblage, the following correlations are sug- 

 gested by genus or species : 



Richmond or younger — Dicoelosia 



Cincinnatian or Trenton — Catazyga 



Leptaenid (Undet. genus B) 



Trenton or upper Wilderness — Anoptambonites cf . A. grayae 



Wilderness or Porterfield — Ptychopleurella cf . P. lapworthi 



Diambonia cf. D. anatoli 

 Xenambonites cf . X. revelatus 



Cyclospira and Christiania are typical Middle Ordovician genera, 

 which range, however, into the Late Ordovician. The Late Ordovician 

 occurrence of Ptychoglyptus may be questioned, but it is well known 

 in Middle Ordovician strata. Although the age of this fauna is open 

 to review, it is clearly either late Middle or Late Ordovician. 



The total aspect of the assemblage is undeniably Caradocian. Per- 

 haps future collections will provide evidence either to extend the 

 ranges of additional Middle Ordovician forms into the Upper Ordovi- 

 cian or to document the occurrence of Dicoelosia in older beds. 

 Dicoelosia may join Austinella and Catazyga as genera now known to 

 have their beginnings in the Middle Ordovician. 



The only coral in the collection was identified by W. A. Oliver, Jr. 



