NORTH AMERICAN EARLY TERTIARY BRYOZOA. 501 



Historical. It is in this group as defined by Waters that the two genera 

 Retepora and Sertella created by Jullien in 1903 may be classified. Following 

 are their descriptions : 



^Retepora, Smitt 1867. Orifice transversely oval, deprived of denticules, an 

 internal border to the ovicell and a spiramen on the frontal. Genotype: Retepora 

 cellulosa Linnaeus-Smitt, 1867.'' 



If the form of the operculum corresponded to this form of the apertura, the 

 genus Retepora might be admitted into these limits, but the operculum of the geno- 

 type published by Waters in 1900 (see fig. 141) is identical with the other opercula 

 of the same group and not at all elliptical. 



"Sertella Jullien, 1903. Orifice elliptical with large transversal diameter, of 



which the anterior lip or anter is festooned and the posterior or poster is smooth 



and curvilinear; these two lips are separated from each side of the orifice by a very 



delicate and fragile cardelle. The frontal is here smooth and with some origells 



(=areolar pores). Genotype: Retepora Beaniana King, 1846." 



We are ignorant regarding to Avhat functions the festoons of the anter corre- 

 spond exactly and it does not seem possible to us to accept a genus based on a 

 character so insignificant. On the other hand, the presence of areolae indicates a 

 special mode of calcification, a perfectly distinct function. Jullien's genus may 

 therefore be maintained, but with this essential character. The study of the frontal 

 of the Eetepores has not yet been made with much care, and it is prudent to await it. 



We are not certain that the reteporidan pore may really always be a spiramen, 

 for Waters indicated an ascopore for Retepora crassa Busk, 18S4. Our American 

 species belong to this group, as defined by Waters. 



RETEPORA RAMOSA, new species. 

 Plate 65, figs. 15-25. 



Description. The zoaritim is free, somewhat compressed, branched, dichoto- 

 mous: it contains only three or four longitudinal rows of zooecia. The dorsal is 

 smooth or very finely granular; the vibices are transverse, irregular, very little 

 salient; some pores are disseminated between them. The zooecia are indistinct; the, 

 frontal is smooth and convex. The apertura is deeply imbedded, hardly visible; 

 its anter is finely denticulated: the peristomice is ogival with a concave lower lip; 

 the spiramen is an elongated slit, often united to the peristomice. The ovicell is 

 hyperstomial, very deeply imbedded in the distal zooecia. hardly salient, smooth; 

 it is perforated by an upper slit. 



Measurements. Peristomice , 



Variations. On each side of the apertura there are usually some very salient 

 tuberosities (fig. 18). The vibices are often replaced by furrows (fig. 20) on the 

 same zoarium; then the small dorsal pores disappear. The ovicell is very fragile; 

 the rupture of its frontal brings about the formation of a false slit (figs. 19, 21) ; 

 its orifice is absolutely buried: it is never closed by the operculum (fig. 24). 



