176 



BULLETIN 100, UNITED STATES NATIONAL MUSEUM 



The operculum is identical with that of Stomhypselosaria. 



Not a single ovicell of the old species has been figured and Mac- 

 Giliivray, 1895, alone noted broken ovicells on M. angustiloba. We 

 have observed beautiful ovicells on the fossil forms of the latter from 

 Australia and on M. acutimarginata . 



In its operculum and its cylindrical zoarium, Mesostomaria mag- 

 nified is, according to Busk, an intermediate species. All the recent 

 species come from very deep water. 



MESOSTOMARIA STRICTORAMAE Canu and Bassler, 1927 



Plate 21, figs. 7-9 



1927. Mesostomaria strictoramae Canu and Bassler, Classification Cheilosto- 

 matous Bryozoa, Proc. U. S. Nat. Mus., vol. 69, art. 14, p. 5, pi. 1, fig. 4. 



Description. — The zoarium is free, dichotomous with compressed 

 narrow fronds. The zooecia are distinct, separated by a deep 



Fig. 50. — Genus Mesostomaria Canu and Bassler, 1927 



A-G. Mesostomaria (Melicerita) atlantica Busk, 1884. A. Zosrium, natural 

 size. B. Group of zooecia, X30. C. Portion of the operculum on the aperture. 

 D-F. Orifices of M. atlantica (D), M. charlesworthi (E), and M. angustiloba 

 (F), showing relative proportions. (A-F, after Busk, 1884.) G. Longitudinal 

 section, X12, showing the position of the ovicell. (After Waters, 1889.) 



furrow, hexagonal; the mural rim is wide, especially laterally, convex, 



smooth, attenuated inferiority where it unites with the eryptocyst. 



The apertura is submedian; semielliptical, transverse, surrounded 



by a thin, salient peristome; its proximal border frequently bears 



two very small denticles. The ovicell is a little convex, transverse, 



smooth, fragile; its orifice is very large and placed obliquely above 



the apertura. 



Measurements. — 



. fk = 0.05mm. ~ . \Lz = 0.24-0.28 mm. 



Apertura , AO nn Zooecia , 00 



[la = 0.08-0.09 mm. U2 = 0.28 mm. 



Affinities. — This species is distinguished from the other known 



species by its narrow almost cylindrical branches. Our specimens 



were dead and deprived of ectocyst. The ovicelled zooecia are 



joined together by their mural rim. 



