NORTH AMERICAN EARLY TERTIARY BRYOZOA. 
95 
gitudinal rows generally very regular. Apertures occupying the whole of the large 
opesium, quite regularly ovate in shape. Rim or interapertural space narrower than 
the opesia, rounded, sometimes angular in the middle, but oftener with a depressed 
interzooecial suture line, marked with close transverse lines or wrinkles. Taking 
the place of an ordinary zooecium, isolated cells, or, more commonly, two or three 
in longitudinal sequence, occur which differ from the rest in having a convex cover 
with a narrow median slit, and above the slit a linear crescentic impression. 
These cells may represent an unusual type of ooecia, but more probably are to be 
considered as a form of vicarious avicularia or vibracula. 
“ The specimens upon which the species is founded are divisible into two 
varieties, one with smaller zooecia and opesia and thicker Avails than the other. 
Measuring longitudinal^ the former has four and one-half zooecia in 2 mm., the 
other only three and a half. Diagonally one has six, the other five in the same 
space. Thickness of zoarial sheet not exceeding 0.2 mm.” 
A restudy of the types shows Ulrich’s description to be exact. Besides the 
abnormal zooecia pointed out by this author we have noted certain zooecia with 
double mural rim, these having undergone total regeneration. It is still impossible 
to place this species genericallv because neither ovicell, avicularia, nor interopesial 
cavities have been observed. The rarity of the specimens does not permit the 
determination of the occurrence of dietellae. 
Measurements. — Opesia. 
\ho= 0.32 mm. 
|/(9=0.20 mm. 
Zooeci 
\Lz= 0.50 mm. 
a 1/3=0.30 nun. 
Occurrence .- — Lowest Eocene (Bryozoan bed at base of Aquia formation) : 
Upper Marlboro, Maryland (very rare). 
MEMBRANIPORINA CANALIFERA, new species. 
Plate 3, figs. 9, 10. 
Description . — The zoarium is incrusting shells. The zooecia are little distinct, 
the neighboring mural rims being intimately joined together; the mural rim is 
hollowed and contains a circular canal about the opesium. which is elliptical and 
median. 
Measurements. — Opesia. 
ho— 0.30 mm. 
/o= 0.20-0.25 
mm. 
Zooecia 
| Lz= 0.37-0.42 mm. 
|/s=0.30-0.35 mm. 
Variations . — This species is well characterized by its circular canal, the use 
of which is unknown. Perhaps it contained glands analogous to those which 
Waters 1 has described in Adenifera ( Memhranipora ) armata Haswell, 1880. In 
the young zooecia this canal is invisible and closed. The calcified zooecia have a 
small linear orifice. 
It is impossible to class this species genericallv, for neither ovicell nor intero- 
pesial cavities have been observed. 
1 1913. Waters, Marine Fauna of British East Africa and Zanzibar. Cheilostomata, Proceedings 
Zoological Society, London, 1913, p. 486, pi. 71, fig. 91. 
