646 



BULLETIN 106, UNITED STATES NATIONAL MUSEUM. 



In the first alternative we would be obliged to create a new work for the zoo- 

 ecial ramifications which would change the description of most of Ulrich's genera 



E x25 



FIG. 208. Mesopores. 



A. Longitudinal thin section, X 25, of Tretocycloecia f attenuata Ulrich, 1882. The rneso- 

 pores are short and few. B. Longitudinal thin section, X 25, of Heteropora avails new species. 

 The mesopores are very short. C. Longitudinal section of Sparsicavea carantina D'Orhigny. 

 (After Gregory.) The zooecia are club-shaped and the walls are simple. D. Longitudinal sec- 

 tion of Ascosoecia (Zonopora) arborea Koch and Dunker, 1837. (After Pergeus, 1899.) The 

 mesopores are ramified. E. Longitudinal section of Parleiosoecia jacksonica, new species, X 25, 

 showing branching mesopores with vesicular walls. 



and species. In the second, on the contrary, very few descriptions would have to 

 be changed. By application of the principle of least change we have thought that 

 the restriction of the term " mesopore " to zooecial ramifications would be preferable 



