290 BULLETIN 11, UNITED STATES NATIONAL MUSEUM. 



pores. The latter form the most noticeable character in thin Sec- 

 tions, where, in the tangential especially, they are so large that 

 the place of an ordinary mesopore is often occupied by one. Four 

 acanthopores usually surround a zooecium, although six or seven 

 sometimes occur. Mesopores are likewise numerous and so large that 

 in tangential sections they are often distinguished from the true 

 zooecia with difficulty. In vertical sections the difference in tabula- 

 tion will of course readily distinguish the two. The walls of both 

 zooecia and mesopores are quite thick for such a form of growth, in 

 fact, with the exception of size of zoarium, H. pygTns&um is an 

 exceptionally well developed species. The tabulation of zooecia and 

 mesopores is shown in figure 176 d, while an idea of the relative size 

 arrangement, and number of mesopores as well as the structure of walls 

 and acanthopores may be had from figures 176 5. and c. 



None of the other species of Hemiphragma has such well developed 

 acanthopores, and this character alone will serve to distinguish the 

 species. 



Occurrence. — Apparently rare in the Chasmops limestone near 

 Bodahamn, island of Oeland, Sweden. 



The figured type and thin sections are in the collection of the 

 British Museum. 



HEMIPHRAGMA MULTIPORATUM, new species. 

 Text fig. 177. 



Although but a few examples of this species have been seen, its 

 characters are so distinct from all other species of the genus that no 

 difficulty should arise in distinguishing it. The zoarium in the type- 

 specimen is a flattened, hemispheric mass, which, before thin sections 

 were cut from it, was 20 mm. in diameter and about 7 mm. high. As 

 usual in zoaria of this shape, the base is slightly concave with a con- 

 centrically wrinkled epitheca. The celluliferous surface is smooth 

 but shows distinct maculae composed entirely of mesopores, at 

 intervals of 4 mm., measuring from center to center. The zooecial 

 apertures are thin-walled, polygonal, and are completely isolated by 

 one to three rows of angular mesopores. About four zooecia occur 

 in 2 mm., although the diameter of a single zooecium averages 0.30 

 mm. Acanthopores are absent entirely, but mesopores are exceed- 

 ingly abundant. In the maculae seven rows of mesopores may be 

 counted, but in the intermacular spaces one or two rows usually 

 separate neighboring zooecia. 



Excepting the numerous mesopores, the internal structure is quite 

 similar to other massive forms of the genus. The mesopores are 

 closely tabulated with straight partitions, while the zooecia have the 

 usual semidiaphragm projecting from either wall and averaging two 

 in a tube diameter in the crowded portions. The very numerous 

 mesopores, however, form the most striking feature of both vertical 



