78 BULLETIN 11, UNITED STATES NATIONAL MUSEUM. 



are more constant. The most obvious feature of thin sections is the 

 unusual number and size of the connecting pores, which give almost 

 a spongy aspect. The views seen in tangential sections are shown in 

 figure 19 l, c, d, where it may be noticed that the lunarium is not 

 clearly outlined from the rest of the zooecial wall. The mural pores 

 are perhaps shown more clearly in vertical sections, especially under 

 a high power of magnification, as in figure 19/. A few delicate 

 diaphragms placed irregularly are developed in the tubes. 



Ceramopora spongiosa is the oldest known species of the genus 

 and differs from all other forms in its few mesopores, large, indistinct 

 lunarium, and numerous connectuig pores. 



Occurrence. — Not uncommon in the Wassalem beds (D3) at 

 Uxnorm, near Keval, Esthonia. 



Holotype.— Cat. No. 57189, U.S.N.M. 



Thin sections of the type-specimen are in the collections of the 

 British Museum. 



CERAMOPORA INVENUSTA, new species. 

 Plate 6, fig. 3; text fig. 20. 



This bryozoan presents the most unusual surface characters of 

 any species known to me, indeed, the zooecial and mesopore walls 

 are so irregular and bear so many knob-like acanthopores or granules 

 that specimens show considerable resemblance to certain sponges or 

 to stromatoporoids. This unusual appearance pertains only to the 

 mature portions of the zoarium, for young specimens have the usual 

 imbricated cells and lunayia of a ceramoporoid. 



The zoarium is incrusting; the type-specimen, an expansion over 

 5 cm. long, is growing upon a large gastropod, while other examples 

 are incrusting ramose bryozoans. The zooecial surface is smooth, 

 with distinct maculae of thick-walled mesopores distributed at inter- 

 vals of 4 to 5 mm. The zooecia are large, 3 to 4 in 2 mm., direct, and, 

 except in young stages, show little trace of a lunarium. The aper- 

 tures are irregularly rounded and are frequently indented by the 

 expanded zooecial walls. The latter are thick but the thickness varies 

 on account of the presence of numerous large, granular-like acantho- 

 pores. Whenever one of these structures is developed, the walls 

 expand to accommodate it, thus giving the irregular or indented effect 

 seen at the surface and in tangential sections. Such granules or 

 modified acanthopores are known in a number of ceramoporoids, 

 especially in certain species of Ceramoporella, but they are unusually 

 well developed in the present form. Mesopores are numerous and 

 sometimes isolate the zocEcia completely. 



Tangential sections bring out particularly the tliick, irregular cell 

 walls and the numerous large granules or acanthopores. The luna- 

 rium, although scarcely distinguishable, is represented in such sec- 



