28 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I48 



of Stenoscisma probably assured that the shell settled beak foremost ; 

 the heavy posterior of Camerisma and Cyrolexis probably also helped 

 maintain that attitude. The great width and high vaulted fold of spe- 

 cies such as Camerisma pentameroides or C. prava probably helped the 

 shell settle with the pedicle valve down. 



The orientation illustrated by Ivanova ( 1949, fig. 30) with the ped- 

 icle valve down and the commissure slanted upward, would have been 

 advantageous for spirolophous forms whose incurrents were antero- 

 lateral and median, and excurrents mostly median as illustrated by 

 Rudwick (1962, p. 599). Frequent changes in location and position 

 probably were necessary to keep the shells in unfouled environments 

 (Rudwick, 1962, p. 608). 



SUMMARY 



Early species in both families of the Stenoscismatacea lived attached 

 by the pedicle throughout life. Later species of Stenoscismatinae lived 

 attached as juveniles but broke free to live on the substrate as adults. 

 Species in the Torynechinae, however, adopted the former habit and 

 remained attached throughout life. 



Individuals of some species of the Atriboniidae seem to have lived 

 free on the substrate for much of their lives, but juvenile specimens of 

 Camerisma are unknown so their early habits remain undetermined. 

 Although the smallest known specimens of Cyrolexis have no pedicle 

 foramen and must have lived free, these are not young juveniles. 

 Therefore, an unattached habit is not clearly demonstrated for the 

 early growth stages. 



