44 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 1 39 



deltidial plates are conjunct but they do not overlie the umbo of the 

 brachial valve as in Hemithyris and several other genera. They are 

 concave and lie ventrally to the umbo of the brachial valve. 



The teeth are large, corrugated and not buttressed by dental plates. 

 Instead of dental plates a thickening extends posteroventrally but 

 does not meet the floor. I have never seen immature specimens and 

 therefore cannot say whether or not dental plates existed in the 

 young as in some other genera. 



The pallial marks of the pedicle valve are like those of His- 

 panirhynchia and Basiliola. In the one specimen showing these marks 

 the course of the sinuses appears as an elevated ridge rather than a 

 depression. This bifurcates near midvalve as in the genera mentioned. 



The great thickening of the apical region of the brachial valve ob- 

 scures many of the details of the cardinalia that can only be cleared 

 up by a study of young specimens. These are not available in the 

 National collections. The true nature of the crural bases is not known, 

 whether they attach to the median ridge or to the valve floor or 

 whether they have supports that extend dorsally. 



Thomson (1927, p. 157) assigned Hemithyris columns Hedley 

 and H. sladeni Dall to his genus Aetheia even though they differed to 

 some extent from the fossil genus. Because of its anterior costation 

 and the bulbous brachial valve the latter of these two species is here 

 placed in Rhytirhynchia, and the former, because of its nearly equally 

 deep valves, among other characters, is placed in Eohemithyris. 



In their correction of brachiopod homonyms in 1951, Cooper and 

 Muir-Wood suggested that Thomsonica Cossmann, 1920, should be 

 substituted for Aetheia because the latter name is preoccupied by 

 Aethia Merrem 1788 (Aves). It is now the sense of the Zoological 

 Commission as outlined in the Copenhagen Proceedings (Hemming 

 1953, Article 34, paragraph 153, p. 78), that these two names are not 

 in conflict. It is therefore necessary to return to Aetheia and reject 

 Thomsonica as Thomson did in 1927 (p. 156). 



Genus PATAGORHYNCHIA Allan, ig38 



Plates 6, A, 21, B 



Patagorhynchia Allan, Rec. Canterbury (N.Z.) Mus., vol. 4, No. 4, p. 199, 1938. 



Subcircular to subpentagonal in outline; inequivalve, the brachial 

 valve having the greater depth ; anterior commissure uniplicate, the 

 fold of the brachial valve being moderately strong. Surface costellate, 

 lamellose to imbricate. Beak short, nearly straight, bluntly pointed; 

 foramen minute, submesothyrid, deltidial plates conjunct and form- 

 ing a concave plate. 



