14 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I39 



Pettit (1950, 1954), in revising the Cretaceous rhynchonelloids of 

 Great Britain, described some details of their interior but his work is 

 disappointing in this respect. In some instances the interior was de- 

 scribed by serial sections when direct preparations should have been 

 less time consuming, easier to make, and far better understood. Owen 

 (1955, p. 369) recently described a method for making serial sections 

 of brachiopods preserved in chalk. In the writer's opinion the serial- 

 section method should be a last resort when all others fail. Chalk 

 brachiopods are easy to prepare directly. The serial-section method is 

 destructive of material and the interior characters may be obscured by 

 old age growth and inner injury. Sectioning is far less satisfactory 

 than direct observation unless it is the only course that can be taken. 



Rzhonsnitzkaia (1956, p. 125) presented an abstract and outline 

 of a new classification of the order Rhynchonellida of Moore 1952. 

 This classification is more elaborate and complete than any hitherto 

 published but the families are not defined and the characters on which 

 they are based are not stated. Family splitting of the rhynchonelloids 

 has been so long needed that the characters of some of Rzhons- 

 nitskaia's new families and subfamilies are quite obvious. For a few, 

 however, they are not so clear. Among the younger rhynchonelloids 

 the only new category introduced is the Hemithyrinae, which will 

 probably receive general acceptance, and is here elevated to family 

 status. 



FAMILY AND GENERIC ARRANGEMENT AND CHARACTERS 

 This brief survey of rhynchonelloid classification indicates that 

 fundamental work is still to be done on the group. These shells are 

 difficult, but they can be made to yield good interiors by simple methods 

 of manual preparation or by serial sectioning. The writer attempts 

 below to group into families the Recent and Tertiary rhynchonelloids 

 on the basis of their interior details combined with features of the ex- 

 terior. The cardinalia characters in their over-all pattern are, in ac- 

 cordance with his work on the orthoids, triplesioids, pentameroids, and 

 several other groups, regarded as of family rank. Some details of the 

 cardinalia are generic but mostly they help to define families. The 

 generic characters are found in minor interior details combined with 

 ornamentation features and beak characters of the pedicle valve. This 

 is well shown by the number of genera in the Paleozoic that have the 

 internal characters of Camarotoechia but vary in external form and 

 ornamentation : Paraphorynchus, Camarotoechia, and Pugnoides are 

 examples. The principle is well exemplified by the families described 

 below. 



