ART. 14 FOSSIL AND KECENT BRYOZOA CANTJ AND BASSLBE 71 



,, , „ ^ \Jia = 0.20 mm. 



Measurements. — Aperture^, „ „„ 



^ Ua. = 0.20 mm. 



„ . [Zs = 0.85 mm. 



Variations. — The operculum is never rigorously orbicular; it is 

 somewhat elongated or a little transverse; it always bears two large 

 very thick chitinous bands; their inferior extremity is exactly at the 

 level of the indentations of the aperture which mark the axis of 

 rotation of the operculum. This arrangement is quite visible on our 

 photograph, but because of desiccation, the operculum is inverted, 

 the poster being visible; when the polypide extends its tentacles, the 

 anter becomes erect and the poster is embedded in the zooecium. 

 The operculum is very fragile and its movements are limited by two 

 small lamellae (proximal and distal) quite visible at the bottom of 

 the peristome. The size of the operculum renders its preparation 

 very difficult; it is deformed and torn very easily. 



a- 



o 



D 



Fig. 11.— Opercular. Exechonella pumicosa, new species. A. Somewhat elongated 



OPERCULUM, X 85, SHOWING THE AXIS OF ROTATION (or) B. PUELLINA FLO RID ANA SMITT 

 1873. A MUCH CHITINIZED operculum, X 85. C. FiGULARIAf AMPLA, NEW SPECIES- 



Operculum, X 85. D. Stenopsis fenestrata Smitt, 1875. Operculum X 85. E- 

 Trypostega venusta Norman. Operculum, X 85 



The cellule a of our photograph shows that the operculum is not 

 attached either to the subadjacent ectocyst or to the compensatrix. 

 We do not know yet if the latter exists on the interior of the zooe- 

 cium under the ectocyst, or perhaps if the space between the frontal 

 and the ectocyst replaces it in order to form a special hydrostatic 

 system. 



The similarity of the operculum with that of the Hippoporae 

 seems to indicate that there is really an interior compensatrix, but 

 the anatomical study alone can furnish positive arguments. 



We have found two species of this genus in the American Claiborn- 

 ian and Jacksonian but the geographic distribution of the genus is 

 much greater. We have noted it in our monograph on the PhiHp- 

 pine bryozoa as present in France (Lutetian, Aquitanian, Burdigalian) 

 and in Australia (Miocene) . Exechonella pumicosa is the third recent 

 species which we have recognized. 



Affinities. — This species differs from ExecJionella magna MacGilli- 

 vray, 1895, in its smaller zooecial dimensions and in its much more 

 porous frontal. 



Occurrence. — Fowey Light, 15 miles south of Miami, Fla.; 40 fms. 



Holotype.— Cat. No. 7838, U.S.N.M. 



