Maryland Geological Survey 275 



apart or about 7 in 5 mm. The appearance of some of these partitions 

 in thin sections seems to indicate that they were centrally perforated. 



Compared with other incrnsting species of Liodema, this pretty form is 

 distinguished by its comparatively large zoa-cia and unusually numerous 

 small mesopores. As figured,' L. (Fistulipora) parasiiicum Hall from 

 the New Scotland beds of New York, has a similar method of growth but 

 its zooecia are smaller, its mesopores larger and more numerous, and its 

 acanthopores apparently quite inconspicuous. 



Occurrence. — Helderberg For:nl\tiox, Keyser Member. Keyser, 

 West Virginia. 



Collection. — U. S. National Museum. 



Genus STENOPORA Lonsdale 

 SteXOPORA (?) INCRUSTANS n. sp. 



Plate XLII, Figs. 11-16; Plate XLIV, Fig. 6 



Description. — Zoarium a thin crust, 1 mm. or less in thickness, gen- 

 erally growing on corals ; composed, so far as seen, of but a single layer. 

 Surface even, with distinct groups of much larger zooecia distributed at 

 intervals of about 4 nun., measuring from center to center. Zooecia 

 polygonal, thin-walled, angular, counting from the center of a macula, 

 7 to 8 in 2 mm. Well-preserved examples sometimes show small acantho- 

 pore-like elevations at the angles and occasionally between them. 



Tangential sections present various appearances according to the ma- 

 turity of the specimen sectioned. Specimens usually found show small 

 acanthopores at the angles of the walls, the latter being thin with their 

 boundaries well marked and the intervening space either clear or faintly 

 dotted. In a fully matured zoarium, the walls are rather thick, the angles 

 of junction occupied by acanthopore-like dark spots and the inner half of 

 the wall by smaller dots arranged either irregularly or in a manner trans- 

 verse to the wall, in the latter case appearing as dark transverse lines. 



Vertical sections show that tlie bend from the immature region to the 

 mature is not abrupt and that in the latter region a few apparently 



^ Nat. Hist. N. Y., Pal., vol. vi, 1887, pi. x.xili, fig. 4. 



