48 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I39 



even in old and obese specimens. This makes a ready distinction and 

 helps to show that septate specimens from the West Coast Tertiary 

 of the United States are not referable to Hemithyris where some of 

 them have been placed. 



The name Hemithyris has been applied to many Tertiary and 

 modern species without regard to geographic realm or biological con- 

 siderations. Many smooth species have been referred here and some 

 plicated species have also been given this name. The ornament of the 

 genus is so distinctive that confusion with other genera should not 

 occur. Hemithyris as now defined appears to be confined to the 

 Northern Hemisphere. Most of the species assigned to this genus 

 from the Southern Hemisphere clearly belong to other genera. As 

 explained above it is difficult to place the rhynchonelloid species gen- 

 erically from descriptions which do not include the interior details. 

 It has thus proved impossible to reassign many of the species now 

 described as Hemithyris or placed in that genus. 



NOTOSARIA Cooper, new genus 

 (Gr. notos, south) 

 Plates 6, B, 22, C 



Subpentagonal in outline, usually widest at the middle ; inequivalve, 

 the brachial valve having the greater depth and convexity ; anterior 

 commissure uniplicate ; brachial valve fold usually low. Surface 

 costellate ; costellae crossed by growth lines and growth varices only. 

 Beak short to moderately long, nearly straight to suberect ; foramen 

 large, incomplete, hypothyrid ; deltidial plates vestigial to prominent, 

 disjunct; beak with thick, transversely striated apical plate. 



Pedicle valve interior with large corrugated teeth supported by 

 short receding dental plates ; muscle field large, wide and flabellate, 

 lobate anteriorly and leaving adductor scars open to the anterior. 

 Pallial marks consisting of numerous anteriorly directed channels. 



Brachial valve interior with deep, coarsely corrugated sockets and 

 overhanging, thick socket ridges ; crura of radulifer type moderately 

 long, horizontally flattened and attached to socket ridges without 

 outer hinge plates. No inner hinge plates. Pallial marks as in the 

 pedicle valve. Cardinal process transversely widely triangular, 

 thickened and somewhat elevated. Median ridge short, low, not reach- 

 ing the apex. 



Type species. — Terebratula nigricans Sowerby, Proc. Zool. Soc, 

 p. 91, 1846. 



