12 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 139 



RHYNCHONELLOID CLASSIFICATION 



Very few comprehensive works have ever been written on the 

 rhynchonelloids. The first to have attempted a detailed classification of 

 these difficult shells was Rothpletz (1886), who divided them into 

 seven species groups and numerous subdivisions of these groups based 

 on exterior details. Although Rothpletz carefully defined the interior 

 of some of the Jurassic rhynchonelloids, using strictly modern meth- 

 ods, he did not bring the information into his classification. Some of 

 Rothpletz's groups and subdivisions bring together species now 

 known to have nothing in common except exterior form. Besides over- 

 looking details of anatomy in his classification, Rothpletz also com- 

 posed unlikely assemblages from various parts of the geological 

 column. 



Bittner's (1890, 1892) great works on the Triassic brachiopods 

 defined in exquisite detail some of the rare and unusual spiriferoids 

 but neglected interior features of the rhynchonelloids except for a 

 few forms. The Triassic rhynchonelloids are a prolific lot and will 

 amply repay in new information a modern, detailed study. Bittner 

 added only a few genera but left many for the future. He, too, was 

 content to work chiefly on exterior details even though the method of 

 serial sectioning was well known and even used by him in some cases. 



Hall and Clarke (1894) described many rhynchonelloid genera but 

 never made a serious attempt at classification. They did, however, 

 show the importance of internal characters and described these details 

 in many Paleozoic genera. 



Weller (1910) used the serial-section method to make known the 

 details of many rhynchonelloid genera, but he did not go beyond 

 genus making. His work was important for showing that a combina- 

 tion of interior and exterior details is necessary for the correct elucida- 

 tion of rhynchonelloid descent. He indicated several genera that had 

 interior details like those of Camarotoechia but were quite unlike that 

 genus in exterior details. He had, therefore, no other choice than to 

 create new genera for them. 



The greatest strides in the understanding of the rhynchonelloids 

 came in Buckman's classic work on the Jurassic brachiopods of Burma 

 and Great Britain. Buckman also proliferated genera more than any- 

 one before him. In his work he relied almost wholly on exterior 

 characters, first on the kind of ornamentation and then on the type 

 of folding of the anterior commissure. These features were supple- 

 mented by some details of the interior such as the septa and the 

 muscle scars which were exhibited by a process of calcining the shells. 



