MARYLAND GEOLOGICAL SURVEY 219 



and with smaller, subcircular or oval apertures and more or less thick 

 walls in fully matured examples ; arrangement of apertures rather regular 

 in rows about small solid spots, in the immediate vicinity of which the 

 zoo2cia may be of larger size than elsewhere; seven to nine in 3 mm. 

 Interspaces apparently solid and generally with shallow irregular depres- 

 sions in most specimens, but in very young stages a variable number of 

 irregular mesopores may be recognized. Acanthopores numerous, two 

 or more to each zocecium, situated in the angles of junction and inter- 

 spaces, and increasing in size with age. They are large and a conspicuous 

 external feature of well-preserved mature examples. 



" Internal Characters: In the axial region of vertical sections the tubes 

 have thin and irregularly fluctuating walls, and few or no diaphragms. 

 The latter are complete here and the proximal end of the tube expands 

 to full size with unusual rapidity. In the peripheral region, which is 

 narrow and abruptly distinguished from the axial, the walls are more or 

 less thickened, and the tubes intersected by semi-diaphragms, about four 

 in 0.5 mm. I have satisfied myself that all the transverse partitions in 

 this outer part of the zocecial tubes are really incomplete. That many 

 may appear entire in sections is only because their inner edge happens 

 to be vertical instead of horizontal. Mesopores are difficult to make out 

 in these sections, being short and usually filled, in part at least, with 

 solid tissue. In the axial part of transverse sections the tubes are un- 

 usually irregular and their walls comparatively thick." Ulrich, 1893. 



Occurrence. CHAMBERSBURG LIMESTONE (Echinospherites bed). Sev- 

 eral localities in southern Pennsylvania and at Pinesburg Station, Mary- 

 land. Black River and Early Trenton of the Upper Mississippi Valley. 



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



Genus DIPLOTRYPA Nicholson 



DlPLOTRYPA ? APPALACHIA n. Sp. 



Plate XLVII, Figs. 9-11 



Description. Zoarium a small hemisphere or subconical mass averag- 

 ing 20 mm. in width and 10 to 15 mm. high. The under surface exhibits 



