10 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 139 



hinge plates. These do not seem to constitute a septalium in the true 

 sense of the word as defined by Leidhold (1928, p. 11) who says that 

 the median septum divides to produce the chamber. Wisniewska 

 (1932, p. 6), on the other hand, states that the septalium of the Meso- 

 zoic rhynchonelloids is formed by internal inflection of the hinge plate 

 to meet the median septum. This seems to be the method of formation 

 of this structure in Frieleia rather than division of the median septum. 



The method suggested by Wisniewska seems certainly to be the 

 case in Septaliphoria in which it is possible in some specimens to see 

 the median septum between the lateral walls of the apical chamber. 

 The specimen illustrated (pi. 21, C, fig. 6) shows the plates converging 

 to the median septum and bounding a small chamber. In other speci- 

 mens the plates bounding the chamber meet the floor of the valve 

 rather than the median septum (see Wisniewska, 1932, p. 26, fig. 6). 



In Camarotoechia (pi. 4, D, figs. 6-8) the entire structure seems to 

 be different from the Jurassic forms and strongly reminiscent of the 

 orthoids. The sides of the chamber buttress the crura which can be 

 seen buried in excess shell tissue surrounding the plates (Kozlowski, 

 1929, p. 146, fig. 43, A). Division into hinge plates is difficult. The 

 structures of the modern and Tertiary forms with camera seem more 

 like the Mesozoic species than like the Paleozoic. 



EXTERIOR CHARACTERS 



It is usually difficult to evaluate the generic characters of the ex- 

 terior of brachiopods and all workers are not agreed on this evalua- 

 tion. It is, however, quite clear that ornamentation and folding pat- 

 terns are generic in character. 



Ornamentation. — Buckman (1917) and Rothpletz (1886), who 

 made attempts at the classification of rhynchonelloid brachiopods, 

 mostly used the exterior to make genera or species groups which 

 might ultimately become genera. Both of these classifications fail be- 

 cause ornamentation and folding are repetitious in many unrelated 

 stocks. Buckman attempted to make his genera on the basis of a 

 scheme of ornamentation development: those that are smooth and 

 then develop costae, those that are capillate and develop costae and 

 ornate or spinose forms. These characters were combined with shell 

 outline and anterior folding. Buckman, however, failed to determine 

 the characters of the cardinalia. 



Rothpletz (1886) arranged many rhynchonelloid species into groups 

 or "Sippe" having similar external characters. Although he determined 

 the nature of the crura of some species he did not reveal the details 



