248 BULLETIN 77, UNITED STATES NATIONAL MUSEUM. 



LibCLEMA SPINEUM, new species. 

 Text fig. 142. 



Zoarium of small, rounded, branching stems, 6 to 7 mm. in diame- 

 ter. Surface without monticules or conspicuous maculae, but much 

 roughened by unusually large acanthopores. Zooecia polygonal, 

 direct, thin-walled, of average size, about 0.4 mm. in diameter, almost 

 always separated from each other by large, angular mesopores. 

 About three zooecia in 2 mm. The maculae are discernible, usually 



Fig. 142.— Lioclema spineum. a, tangential section, X9, showing relations of zocecu, mesopores, 



AND acanthopores; 6, THE DETAILED STRUCTURE OF AN ACANTHOPORE, X40; C, PORTION OF A TANGEN- 

 TUL SECTION, X20, WITH THE MESOPORES SHADED; d, VERTICAL SECTION, X20. ORTHOCERAS LIMESTONE 

 (B3), ISLAND OF ROGO, ESTHONIA. , 



only in thin sections, by the presence of more numerous mesopores 

 and slightly larger zocEcia. Mesopores thin-walled, often larger than 

 the zooecia but differing from them in having fewer sides. Moreover, 

 the mesopores are frequently closed by the outermost of the num- 

 erous diaphragms crossing their tubes. Acanthopores very large 

 and bluntly rounded, often equaling a zooecium in diameter. 



The relative size and arrangement of the zooecia, mesopores, and 

 acanthopores are well shown in tangential sections. Here the zooecia 

 are seen to be more regularly polygonal than the mesopores and to 

 have slightly thicker walls. The irregularity in shape and frequent 



