8 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I39 



the Jurassic of Poland, more clearly defines these types and adds a 

 fourth, as follows : 



1. Radulifer type. — Crura narrow, recurved toward the ventral 

 valve, widening gradually toward their extremity. This type, charac- 

 terizing the genera Septaliphoria, Rhynchonella, and Cyclothyris, was 

 given the name "radulifer" by Rothpletz. 



2. Falcifer type. — Crura with a large suspended crural plate, touch- 

 ing the bottom of the valve only near its summit. This is the "falcifer" 

 type of Rothpletz characterizing the genus Lacunosella. 



3. Septifer type. — Crura short with the crural plates supported at 

 the bottom of the valve and extending for about one-third the valve 

 length. This is the "septifer" type of Rothpletz affirmed by us only 

 in the genus Septocrarella. 



4. Arcuifer type. — Crura with large bases separated from each 

 other and curved so as to turn their concave sides toward the middle, 

 the extremity turned toward the ventral valve and terminated by a sort 

 of small crural plate in the form of a hammer. This type of crura, 

 seen in the genus Monticlarella, may be called "arcuifer." 



Muir-Wood (1934, p. 526; 1936, p. 14) added a fifth type as a 

 result of her work on Mesozoic brachiopods : 



Calcarifer crura. — ". . . The crura consist of two flattened, 

 curved, posteriorly concave laminae which project from the hinge- 

 plate into the cavity of the pedicle valve. These laminae each unite 

 with a second curved lamina which appears to be suspended from it 

 and projects dorsally like a spur. A ventral extension of the second 

 lamina terminates in a hook-shaped process, the apex of which is 

 directed medianly." Kallirhynchia and Rhynchonelloidella possess 

 this type. 



Among the Tertiary rhynchonelloids considered herein five types 

 of crura are distinguishable, three of which have been identified 

 among Mesozoic genera and have been named. Two types have not 

 been named or described among the Mesozoic genera. 



Of the three named types Hemithyris belongs to the group having 

 radulifer crura. These are long, slender, and curved but have a hori- 

 zontally flattened, bluntly pointed distal extremity. The Hemithyris 

 crus is strengthened by a narrow ridge on the anterior side. The 

 radulifer type of crus is not common among Recent and modern 

 genera. 



The second type of crus known in the Mesozoic and present among 

 modern and Tertiary genera is that characteristic of the Basiliolidae 

 and named falcifer type. The Basiliolidae are all characterized by 



