54 



SMITHSONIAN MISCELLANEOUS COLLECTIONS 



VOL. 57 



Genus MACKENZIA, new genus 



Body elongate, cylindrical. Anterior end with a circle of plates 

 about it (as preserved as casts on the rock). Posterior end slightly 

 contracted, mouth terminal. Anus unknown but probably terminal. 

 Tentacles and interior structure unknown. 



Genotype. — Mackencia costalis, new species. 



The stratigraphic range and geographic distribution are the same 

 as for Laggania (p. 52). 



Fig. 6. — Syiiaptula liydriforDiis (Lesseur). Adult animal. Natural size. 

 (After Clark, 1907, pi. 6, fig. 5.') 



This rare form was first placed among the annelids when the col- 

 lection was unpacked, but with the study of the material preparatory 

 to photographing the different species it was removed to the holo- 

 thurians. The cylindrical form, circle of plates, and banded appear- 

 ance at once suggested a fossil resembling Synaptula hydriforuiis 

 (Lesseur) but without its beautiful tentacles.'' 



' Clark, H. L., 1907, Smithsonian Contributions to Knowledge, Vol 35, pi. 

 6, fig. 5- 



