2 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I30. 



described, nor were specimens available to use in this study. Conse- 

 quently it is possible to assign to their proper genera only some of the 

 known species. It is also known that the interior of a number of 

 species differs from that of any of the genera discussed herein, but 

 these species are represented by too few specimens to make generic 

 description possible. Much therefore still remains to be done in the 

 study of the Tertiary and Recent rhynchonelloids. 



Possibly the biggest handicap in the study of modern and Tertiary 

 rhynchonelloids is the fact that, except in a few instances, the speci- 

 mens are quite rare. Several of the Recent species are known from one 

 or two specimens only, yet their morphological details are unique or 

 sufficiently different from known genera to make it impossible to 

 include them in any of the established categories. 



Some of the Tertiary species are sufficiently numerous for good 

 descriptive work but their describers seldom made any effort to obtain 

 interior details. Davidson (1870) did not describe the interior of any 

 of the Italian Tertiary rhynchonelloids, probably because emphasis in 

 his day was on description of the species. Later authors seemed to 

 be content to assign many of the modern species to Hemithyris regard- 

 less of whether or not the interior or exterior details were in ac- 

 cordance with the generic characters of the type species. In present 

 times emphasis is now placed on interior details because it is on them 

 that the family and frequently the generic characters are based. 



ACKNOWLEDGMENTS 



In any study of this sort it is necessary to ask help of one's col- 

 leagues. I am grateful to all the scientists listed below for their help. 

 Dr. Helen M. Muir-Wood, Deputy Keeper, Department of Palaeon- 

 tology, in charge of the brachiopods in the British Museum (Natural 

 History), furnished a specimen of Compsothyris, photographs of 

 Rhynchonella grayi Woodward, photographs of serial sections of R. 

 polymorpha (Massalongo) and R. bipartita (Brocchi), and casts of 

 the specimens serially sectioned. Dr. A. Vandercammen, Subdirector 

 of the Laboratory, Royal Institute of Natural Sciences, Belgium, 

 furnished a specimen of Mannia nysti Davidson, a rare Belgian 

 species. 



Mrs. Ellen J. Trumbull of the U. S. Geological Survey made avail- 

 able specimens of west coast Tertiary species. Dr. J. H. Peck, Senior 

 Museum Paleontologist of the Museum of Paleontology, University 

 of California, made available a fine suite of topotypes of Eohemithyris 

 which made possible preparations of the inner details of that interest- 



