58 BULLETIN 96, UNITED STATES NATIONAL MUSEUM. 



convexity of the frontal ; they are quite apparent when the prepara- 

 tion is properly inclined. 



The spiramen is little visible in perspective because it is in a plane 

 almost perpendicular to the zooecial plane. 



Occurrence. — Lower Jacksonian: Jackson, Mississippi (rare). 



Ty2)e.—C^t. No. 62603, IJ.S.N.M. 



Genus HASWELLIA Busk, 1884. 



1SS4. Hafiicellia Busk, Report on the Polyzoa collected l^y H. M. S. 

 Challcnyer, pt. 1, p. 171. 



The apertura has its proximal border notched by a very wide 

 rimule not separated from the anter. The frontal is a very thiclc 

 tremocyst. The spiramen is a small salient tube. The zoarium is 

 cylindrical. 



Genotype. — Jlaswellia {Myrlo2oum) austraUensis Haswell, 1880. 



Range. — Tongrian-Recent. 



SEMIHASWELLIA, new genus. 



The zooecia are disposed only on one side of the zoarium; the 

 dorsal bears only avicularia. The frontal and the dorsal are of the 

 same nature and are formed of a tremocyst with sulci. 



Genotype. — Porina prohoscklea Waters, 1888. Range : Jacksonian- 

 Recent. 



This new genus is zoarial; no distinct zooecial function separates 

 it from Haswellia. Nevertheless it has some important zoarial func- 

 tions susceptible of giving generic characters; the very constant 

 presence of small dorsal avicularia seems to be a very good character. 

 The recent specimens are extremely rare and it is still not possible 

 to study them in detail. Species of both flaswellia and Semihas- 

 wellici occur in the Jacksonian of the Southern States. 



Genus GIGANTOPORA Ridley, 1881. 



1881. Gigantopora Ridley, Zoological collections made din-ing survey of 

 H. M. S. Alert. Proceedings Zoological Society London, p. 47. 



The apertura bears a rimule. The frontal is an olocyst. The 

 spiramen is inconstant; it is almost as large as the apertura. 

 Genotype. — Gigantopora lynchoides Ridley, 1881. 

 Range. — Jacksonian-Recent. 



Genus GEPHYROPHORA Busk, 1884. 



1884. Gephyrophora Busk. Report on the Polyzoa collected by H. M. S. 

 Challenger, pt. 1, p. 67. 



The apertura nears a proximal rimule. The frontal is a tremocyst. 

 Genotype. — Gephyrophora polyniorpha Busk, 1884. 

 Range. — Tongrian-Recent. 



