Maryland Geological Survey 279 



and regularly corrugated, with about 15 corrugations in the space of 5 mm. 

 Diaphragms wanting. 



Polygonal zocecia with thin and strongly corrugated walls and the 

 absence of diaphragms are characteristics of this species which readily 

 separate it from other massive bryozoa. 



Occurrence. — Helderberg Formation, Xew Scotland Member. 

 Southwest slope of Elbow Ridge, Washington County ; Dawson. 



Collections. — Maryland Geological Survey, U. S. National Museum. 



Genus STROMATOTRYPA Ulrich 

 Stromatotryfa globul-\ris n. sp. 



Plate XLII, Figs. 1-4; Plate XLVI, Figs. 8, <J 



Description. — Zoarium usually forming globular masses 25 mm. or 

 more in diameter, becoming more or less irregular with age, the largest 

 specimen seen measuring about 170 mm. in its greatest dimension. 

 Zocecial tubes radiating from the base which is usually small and some- 

 times covered with a wrinkled epitlieca. Celluliferous surface even, but 

 exhibiting at regular intervals rather inconspicuous maculae composed of 

 slightly larger zocecia. Zocecial apertures circular or polj'gonal, their 

 shape depending upon the relative development of the mesopores. In 

 younger stages the mesopores are large and apparently never in more than 

 one series between neighboring zocecia, becoming smaller with age, and in 

 the fully matured condition wedging out, the zocecia at the same time be- 

 coming correspondingly larger and assuming the angular shape incident 

 to contiguity. Five zocecia may be counted in the space of 2 mm. and 

 because of the relation between the sizes of the zocecia and mesopores 

 mentioned above, the estimate holds, whatever the condition of the latter. 

 Acanthopores about as numerous as the zocecia, rather well dcNelojied as 

 seen in tangential sections, but, especially in the rather unfavorable pres- 

 ervation of the surface characters prevailing among the specimens seen, 

 not a conspicuous external feature. In thin sections the acanthopores 

 prove to be thin-walled, the lucid spot, as is demanded by the genus Stro- 

 matotrypa, being relatively much larger than in the more common types 



