NORTH AMERICAN' EARLY TERTIAEY. BRYOZOA. 269 



THALAMOPORELLA PRIMA, new species. 



Plate So, fig. 14. 



Description. The zoarium is bilamellar. The zooecin are distinct, elongated, 

 rectangular, and their mural rims are intimately united among themselves; the 

 iTyptocyst is deep, flat, with numerous i reinopores. The apertura is orbicular or 

 somewhat transverse, the poster is narrower than the sinter; it has a large, distal, 

 vestibular arch; the polypidian tube is invisible. The onychocellarium is straight, 

 oval, narrow, and perforated by a single elliptical orifice. 



I A0=0.1_M).15 mm. . |Zs=0.5.">mm. 



Measurements. Opesium 7 Zooecia 7 - , 



[lo =0.1-2-0. 15 mm. |fe=0.3o-0.40mm. 



A-ffin/fics. Only a few specimens of this species have been found. They are 

 difficult to determine for all the species of the genus are quite polymorphic. To 

 us the present form appeared to differ from Thalamoporella rozieri Savigny- 

 Audouin (1826) in its smaller micrcmetric dimensions (?s=0.55 instead of 



0.72 mm.). 



Occurrence. Uppermost Vicksburgian (Byram marl) : Leaf River. Smith 

 County. Mississippi (very rare). 



HoIo/ype.Cat. No. 64265, U.S.N.M. 



Division III. PSEUDOSTEGA Levinsen, 1909. 



There are no parietal muscles. The hydrostatic system is external; there is 

 a special hypostege on each zooecium. 

 The families of this division are : 



Membranicellariidae Levinsen 1909. 



Cellariidae Hincks 1880. 



Coscinopleuridae Canu 1913. 



We are ignorant of the exact working of the hydrostatic system in the species 

 of this division. It is probable that the lateral incisions of the opesium, other- 

 wise very constant, are in intimate relationship with the entrance or egress of the 

 polypide, for they serve as passage for the liquid of the general cavity in the 

 hypostege or vice versa. 



The endocyst covers a hypostege. Its presence is often revealed by supple- 

 mentary calcareous deposits which may always be distinguished by their irregu- 

 larity. 



Other genera certainly belong to this division, but it has not been possible 

 for us to class them in the families cited. It would be absurd to create a special 

 family for each of them since we lack absolutely the necessary anatomical features. 



Here the opesium being entirely dosed by a constant operculum of the same 

 form, becomes a real aperture, as in the Ascophora. 



Family CELLARIIDAE Hincks, 1880. 



KiMiiiuraiiliit (Anatomical). 1900. CALVET. Contribution a 1'Historie naturelle de Bryozouhvs 

 Ectoproetes marines, Montpellier. Mi'in. S, pi. fi, fig. 11 ; pi. S, ft;.'. 14; pi. 10. fig. 4; pi. 11, 

 figs. 10. 11, 12; pi. 12, figs. 7. 8, 9: pi. 13, figs. 12 to 18. 1904. WATERS, Resultats du voyage 

 flu S. Y. lii'lgiru, Brj-nzoa (Expedition .iiitaretique beige), pi. 2, fig. 9. 1909. LEVINSEN Mor- 

 phological and systematic studies on the Cheilostoinatons Bi-yozoa. p. 209, pis, 7 and S 



