222 



BULLETIN 11, UNITED STATES NATIONAL MUSEUM. 



as the most conspicuous feature of the celluhferous face. In S. 

 revalensis these ckisters are outHned by polygonal, raised areas com- 

 posed of mesopores (see pi. 4, fig. 8), but in S. constellata these thin 

 ridges are absent, the rays of the maculae being confluent. The occur- 

 rence of such polygonal areas is not restricted to Stellii^ora because 

 species of Constellaria, such as C. polystomella, and of Dianulites, D. 

 petropolitana for example, Hkewise bear them. Numerous specimens 

 of the two latter species have been examined with the result that the 

 polygonal areas are known to be inconstant in their development. 

 Some specimens have them excellently developed, while others show 

 no trace. Still other examples will have a portion of the surface with 

 well marked areas, and another portion without a trace of them. 



Fig. 123.— Stellipoka eevalensis. a, vertical section, X20; 6, tangential section, X20, illus- 

 trating SfRUCTURE OF TWO EATS OF A CLUSTER. KUCKEKS SHALE (02), BaEON TOLL'S ESTATE, 

 ESTHONIA. 



These thin ridges are composed entirely of mesopores and seem to 

 m.ark out areas of distinct growth. 



In figure 123 the normal internal structure, drawn under the 

 camera lucida, is shown. Figure 123 a represents the very short 

 immature zone in which the zocecia are prostrate, and the mature 

 region of the ordinary zooecia and a part of a macula. Dybowski's 

 figure of the vertical section is rather diagrammatic and fails to show 

 the cyst-Hke tabulse filHng the mesopores. The zooecia proper have 

 straight diaphragms about their own diameter apart in the more 

 crowded portions. Comparing the figure on plate 4 and figure 123, 

 Dybowski's tangential section and the one prepared from specimens 

 in the collection of the United States National Museum are seen to 

 be ahke. The small, rounded apertures are the zooecia, while the 

 large, irregularly shaped openings represent the m-esopores. 



Further notes upon Stellipora revalensis are given under the discus- 

 sion of the next species. 



Occurrence. — Dybowski records his species from zone 1 at Sack, 

 Kuckers, and Reval. The specimens before me come from the 



