NO. 2 BRACHIOPOD SUPERFAMILY STENOSCISMATACEA — GRANT J 



throughout the range of the group. Persistence of this feature through- 

 out the superfamily constitutes evidence for its relationship with the 

 Rhynchonelloidea ; it leads the search for ancestors and descendants 

 to genera that are similarly folded. 



Sulcation. — Only Camarophorina among the Stenoscismatacea has 

 the fold in the pedicle valve. This condition occurs in many groups of 

 brachiopods. A few examples include Sanjuania Amos (Mississip- 

 pian), Paranorella Cloud (Permian), Novella Bittner, Rhynchonella 

 retractifrons Bittner (Triassic), and the Recent genus Neorhynchia 

 Thomson among the Rhynchonellacea ; Brachymimulus Cockerell (Si- 

 lurian) in the Triplesiacea, Parenteletes R. E. King (Pennsylvanian- 

 Permian) in the Dalmanellacea, and Centronella Billings (Devonian), 

 Pseudoglossothyris Buckman (Jurassic) and the modern genus Abys- 

 sothyris Thomson in the Terebratulacea. Recurrence of sulcation in 

 various groups throughout the history of the Brachiopoda indicates no 

 more than generic importance. 



COSTATION 



Costation is a typifying but not identifying character of genera 

 within the Stenoscismatacea. The general trend is toward increasing 

 strength of costation within the superfamily, but earliest known genera 

 are costate, and least costate genera are midway in the range of the 

 superfamily. However, evolutionary trend in the Family Stenoscis- 

 matidae (fig. 3) is toward increasing strength and extent of costation. 



Description. — Costae are present in some genera of the Stenoscis- 

 matacea, absent from others. They are strong or weak, begin at the 

 beaks or anterior to the beaks, and occupy the fold or the flanks, or 

 both. Normally the costae are simple, V-shaped, without bifurcation 

 or intercalation. Only the genus Torynechus has narrow ridgelike 

 costae that increase in number anteriorly by intercalation. Camaro- 

 phorinella and some species of Stenoscisma have occasional bifurcating 

 costae, especially at the sides of the fold and sulcus ; Sedenticellula has 

 narrow, frequently bifurcating costae. 



Costae normally increase in height toward the anterior of the shell, 

 but in Torynechus and Septacamera they are broader and flattened on 

 the anterior slope ; in the former, each costa has a median furrow in- 

 stead of a crest, essentially doubling the number of ribs, as in Un- 

 cinulus or Rhynchopora. The ends of costae project like sharp teeth, 

 serrating the commissure. Externally these serrations produce deep 

 indentations in the edge of the stolidium where it joins the shell. 



Taxonomic importance. — Costae are important taxonomically on 

 two levels. Their presence or absence is important generically ; costae 

 are present in most genera of the Stenoscismatacea, but they are absent 



