34 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I48 



names based on Stenoscismatinae Oehlert ( 1887) were in general use 

 prior to 1961, and should be retained in the interest of stability. She 

 has requested the International Commission on Zoological Nomen- 

 clature to put this name on the Official List of Family-Group Names 

 in Zoology. The Rules require, however, that the pertinent date in this 

 case is the first recognition of the family-group, and this is the date 

 of Waagen's (1883) establishment of the Camerophoriinae. 



EVIDENCE 



Early comparison of internal structures of stenoscismatids with 

 those of pentamerids led to classification of the two groups together. 

 The apparent similarities are striking. The high camarophorium in 

 the dorsal valve of the Stenoscismatacea is nearly identical in shape 

 to the high ventral spondylium of the Pentameracea, and the longitudi- 

 nal profile of the ventral spondylium of the Stenoscismatacea resembles 

 that of the elongate dorsal cruralium of some pentameroids ( Schuchert 

 and Cooper, 1932, pi. 26, figs. 31, 35, 40) . 



Upon analysis, however, the internal structures of the two groups 

 are seen to be unrelated ; the similar-appearing structures are in op- 

 posite valves. The high spondylium of the pentameroids necessarily 

 must have seated the diductor muscles, and muscle scars are visible 

 there (Schuchert and Cooper, 1932, p. 164), whereas the high struc- 

 ture of the Stenoscismatacea is in the opposite valve, and probably bore 

 the adductor muscles on its inner surface. 



The brachial processes of the pentameroids are fused to the septal 

 plates, but in the Stenoscismatacea they extend anteriorly from the 

 edge of a rhynchonelloid hinge plate and are free for most of their 

 length. These processes are considered the same or analogous to the 

 crura of the Rhynchonelloidea, and constitute a strong argument for 

 inclusion of the Stenoscismatacea with that suborder (e.g., Muir- 

 Wood, 1955). 



The most advanced, and in the U.S. National Museum collection 

 the best preserved, genus of the Stenoscismatacea is Stenoscisma. 

 Many species of this genus have well-developed deltidial plates to con- 

 strict the delthyrium and outline the pedicle foramen. Small deltidial 

 plates are visible on well-preserved specimens of Torynechus and 

 Atribonium as well. Deltidial plates are characteristic of most rhyn- 

 chonelloids, but are entirely absent from Pentameroidea (Schuchert 

 and Cooper, 1932, p. 163). 



Permian representatives of Stenoscisma have an elaborate system 

 of bifurcating pallial markings that were well illustrated by King 

 (1850, pi. 8). These resemble the bifurcating pallial systems of some 

 rhynchonelloids and orthoids (Cooper, 1944; Williams, 1956), be- 



