2 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I40 



the resulting picture of morphologic trends and hypothesized lineages 

 discussed below suggest that species of Amplexopora will prove ex- 

 tremely useful in stratigraphic paleontology. 



The genus Stromatotrypa Ulrich, 1893, was investigated in connec- 

 tion with Batostoma, and study of new sections of the type species, 

 S. ovafa Ulrich, 1893, resulted in Stromatotrypa being considered a 

 junior subjective synonym of Batostoma. (See p. 6 and pi. 7, figs. 

 2-4.) 



The genus Acanthotrypella Vinassa de Regny, 1920, was con- 

 sidered to be a junior subjective synonym of Batostoma by Bassler 

 (1935a, p. 54). Study of new sections of the type species, B. variahile 

 Ulrich, 1890, resulted in Acanthotrypella being considered a junior 

 subjective synonym of Amplexopora. (See p. 19 and pi. 7, fig. i.) 



The manuscript was critically read by June Phillips, Yale Uni- 

 versity, N. Spjeldnaes, University of Oslo, and R. Cifelli and P. M, 

 Kier, U. S. National Museum, and many of their suggestions have 

 been incorporated in the final draft. Thin sections were prepared by 

 T. M. Robison of the U. S. Geological Survey. Photography was 

 done by J. Scott of the U. S. National Museum. 



Wall structure and ontogeny of Anaphragma. — The thin zooecial 

 walls in the endozones (immature or axial region of authors) of most 

 trepostomes are either granular or longitudinally laminated and give 

 no indication of whether their deposition took place from one or both 

 sides of the walls. The zooecial walls in the endozones of the type 

 species of Anaphragma, A. mirabile Ulrich and Bassler, 1904, are 

 laminated and contain a dark median line that is connected distally 

 to zooecial boundaries in the exozones (mature or cortical region of 

 authors). These median lines are interpreted as zooecial boundaries 

 in the endozones and are considered to indicate that the walls are 

 transversely laminated and that deposition of the walls took place 

 from both sides (Boardman, 1959, p. 2). Thus, the structure of the 

 walls in the endozones of A. mirabile is thought to support the logical 

 assumption that the walls result from deposition by tissue of im- 

 mediately adjacent zooecia. 



The microstructure and resulting appearance of zooecia, mesopores, 

 and acanthopores of A. mirabile show progressive changes of re- 

 markable magnitude through a thick-walled exozone. The zooecia 

 are assumed to have grown by the addition of skeletal laminae on 

 the surfaces at their distalmost ends, thus adding to the width of the 

 exozone. The width of the exozone in a segment of a fossil zoarium 



