926 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
which to establish a species, and the interior of the brachial valve is unknown. 
This is the earliest Opikina known. 
Genus STROPHOMENA Blainville, 1825 
Strophomena BLAINvILLE, Man. Malacol., vol. 1, p. 513, 1825—HALt and CriarkeE, Pal. New 
York, vol. 8, pt. 1, p. 245, 1892. 
Opikina Witson, Trans. Roy. Soc. Canada, ser. 3, vol. 38, sec. 4, p. 190, 1944; Geol. Surv. 
Canada, Bull. 8, p. 95, 1046. 
Strophomena is an abundant brachiopod throughout rocks that are here as- 
signed to the Wilderness and Trenton stages. This name is applied to convexi- 
concave brachiopods having moderately large muscle fields in the pedicle valve 
which are partially surrounded by a thickening extending anteriorly from the 
dental ridge. Inside the brachial valve the cardinalia are generally small and 
delicate, the median ridge short, and pallial marks not well impressed. Com- 
parison with the genotype, Strophomena planumbona (Hall), shows essential 
agreement in most of the important details. Nevertheless, a fair variety of forms 
has been brought together here under the name Strophomena. Ultimately, some 
splitting of groups is likely, but the collections available in this study are too few 
to make any progress along these lines possible. 
The National Collection is not well provided with specimens of Strophomena 
except from a few localities. The collections from the Arbuckles are excellent, 
but those from the Appalachians are good from only a few places. Wardell and 
Ridley specimens are numerous, but only a few of quality have been taken from 
the Witten or higher beds. Good material from the Central Basin of Tennessee 
was studied, but the collections from New York and Ontario are meager indeed. 
The only regions in which a notable number of species of Strophomena have 
been described are the region about Ottawa, Ontario, and the Plattin area of 
eastern Missouri. The Ontario Black River and Trenton faunas were described 
by Dr. Alice E. Wilson. Many species of Strophomena are described, and two 
genera have been split off from it. In general, the species are not adequately 
illustrated, and the original specimens show evidence of exfoliation. This is not 
ideal material for constructing new species. It has therefore not been possible to 
identify any of the Wilson species outside of New York and Ontario. 
Similar remarks may be applied to Fenton’s descriptions of species of Stropho- 
mena from the Plattin of the Ste. Genevieve County area in eastern Missouri. 
The material illustrated by Fenton is good but the illustrations feature chiefly 
interiors of pedicle valves and occasional other views. No profiles are given, and 
great reliance is put on the interior of the pedicle valve. Fenton relegates a posi- 
tion of unimportance in the classification of species to the shape of the shell, 
wrinkling of the cardinal extremities, the costellation, and thickness. The writer 
believes that even the muscle scars of the pedicle valve of this genus are not re- 
liable because they are so variable. Total available features must be taken into 
account in defining a species of this genus. Few of Fenton’s species are recog- 
nizable in the Appalachians. 
Black River and Trenton Strophomena must some day be studied as a whole 
