100 BULLETIN 16 5, UNITED STATES NATIONAL MUSEUM 



Plate 16 



Figures 1-7. Acanthionella typica Gabb and Horn, 1860 (p. 84). 



1, Zoarium ( X 6) encrusting Coscinopleura digitata and emit- 

 ting three bilamellar branches. 



2, Surface of bilamellar specimen much calcified. The pores of 

 calcification and the formation of new avicularia derange the 

 order of the primitive avicularia. From near Blackwoods- 

 town, N.J. 



3, Marginal zooecia of an encrusting colony. They are identical 

 with the zooecia of bilamellar specimens. 



4, Encrusting zoarium with its ancestrula, which is a small ordi- 

 nary zooecium. 



5, Bifurcated branch, showing the arrangement of the zooecia 

 below the bifurcation. The epicalcification is little intense, 

 and the ovicells are still visible exteriorly. 



6, Bilamellar specimen, showing the progress of epicalcification 

 (from top to bottom). The ovicell is hidden by the avicularia 

 and is visible only by its orifice placed above the apertura. 



7, Young ovicelled branch with regular and little calcified 

 zooecia. The ovicells are large and salient. 



Plate 17 



Figure 1. Dacryopora (?) orbifera, new species- (p. 71). 



The uniserial encrusting type specimen. From Noxontown Mill- 

 pond, Del. 

 2-5. Exochella septentrionalis, new species (p. 79). 



2, The encrusting zoarium with ovicelled zooecia. The ancestrula 

 is a small ordinary zooecium ; the mucron is little salient. 



3, Ancestrular portion of figure 4, showing a membranlporoid an- 

 cestrula surrounded by four avicularia. 



4, A zoarium showing marginal ovicelled zooecia with 1 or 2 oral 

 avicularia. 



5, Ancestrular portion of another specimen. The ancestrula is 

 membraniporoid with 4 spines and surrounded by 2 avicularia. 



6,7. Diplotresis sparsiporosa Ulrich and Bassler, 1907 (p. 72). 



6, Surface of the encrusting zoarium with regular zooecia and 

 containing series and groups of zooeciules. 



7, Portion of a zoarium with irregular zooecia. 



Plate 18 



Figure 1. Hippothva tenuiehorcia Ulrich and Bassler, 1907 (p. 71). 



The encrusting zoarium of narrow, elongate, club-shaped zooecia. 

 2,3. Beisselina intermedia, new species (p. 75). 



2, Median part of the bifoliate zoarium, showing the arrangement 

 of the large avicularia. 



3, Several fragments (natural size) and lateral portion of a branch 

 (X 20). There are 4 to 6 small peristomial avicularia and 3 to 

 5 small frontal avicularia. 



4. Beisselina lonsdalei, new species (p. 77). 



The type specimen, a bifurcated branch (natural size and X 20). 

 Each peristomice is surrounded by 4 or 5 avicularia. The frontal 

 is hidden by 4 to 8 small avicularia. 



