NO. 2 BRACHIOPOD SUPERFAMILY STENOSCISMATACEA — GRANT 25 



they undergo clear phylogenetic trends that would be of major tax- 

 onomic value to earlier genera whose patterns are unknown. 



SHELL STRUCTURE 



Serial sections prepared for study of internal structures reveal no 

 unusual lamination of the shell. The shell of all stenoscismataceans is 

 impunctate, and consists of an outer primary layer of calcite, and an 

 inner secondary layer. No periostracum is visible. Silicified shells show 

 none of the original lamination, and some calcareous shells have been 

 replaced by calcite that also has destroyed the former structure. Cross- 

 sections of the shell are illustrated in plate 6, figs. 4, 4a ; plate 8, figs, 

 lb, 2a; plate 12, fig. Id ; and plate 17, fig. 5a. 



