NORTH AMERICAN EARLY TERTIARY BRYOZOA. 547 



forming a special genus. An artificial subgenus appears to us useful for classifi- 

 cation. 



The only known described species of this genus are Tubucella mammillaris 

 Milne-Edwards, 1836, of the Lutetian-Sannoisian of Europe and TubuceHa pn/ttf- 

 losa Keuss, 1817, of the Priabonian of the Vicentin. We have discovered two 

 species in the American deposits. 



TUBUCELLA MONILIFERA Canu and Bassler, 1917. 



Plate TO, figs. 1S-25. 



1917. Tubucella monilifcra CANU aucl BASSLEB. Synopsis of American Early Tertiary 

 Cheilostorue Bryozoa, Bulletin 96, United States National Museum, p. 63, pi. 5, 

 fig. 9. 



Description. The zoarium is free; the two lamellae are placed back to back 

 and intimately joined; the fronds are broad, compressed, distorted, and branch- 

 ing. The zooecia are much elongated, fusiform, little distinct, surrounded by a 

 collar of large pores; the frontal and the peristomiale are of equal length, sepa- 

 rated by the ascopore and perforated with small hexagonal pores. The peristome 

 is salient, thick, oblique. The avicularia are very rare, large, transverse, elliptical, 

 usually with two denticles for a pivot. 



\Lz= 0.90-1 .00 mm. 

 Measurements. Zooecia -, 



U3=0.32 mm. 



Variations. The zooecia are very constant in their exterior aspect. The 

 larger pores surround the peristomiale and are three times larger than the others. 



Certain fronds bear some zooecia (fig. 20) closed not by the olocyst, but 

 by the tremocyst, the tubules of which have encroached upon the peristome. The 

 physiological function of these zooecia is unknown. 



The avicularia are scattered, are very large, and form a very large frontal 

 (fig. 21), the origin of which is one of the lateral pores of the peristomiale. 



We have often noted before the faculty of the tremocystal buds to transform 

 themselves into avicularia. 



Ovicelled zooecia have been observed and are illustrated in figure 22. where, 

 also, an avicularium with pivot may be noted. 



In the interior (fig. 2-1) we have noted a very thin perforated olocyst sur- 

 mounted by a tremocyst with tubules. The ascopore opens very far from the aper- 

 ture and the peristomie. In comparing the extreme simplicity of this internal 

 structure with the beauty and regularity of the exterior ornamentation, we must 

 admire the splendor of the work of the buds of the endocyst. whose calcareous 

 deposits so successfully modify the aspect of the zooecia. 



Affinities. This species differs from Tubucella mammilaris Milne-Edwards, 

 1S36. in its nonprominent ascopore and the absence of large globular ovicells. 



It differs from Tubucclln ]>apiUosa Reuss. 1847, in the absence of the arched 

 ovicelled zooecia and its much straighter fronds. 



