EAELY TERTIARY CHEILOSTOME BEYOZOA. 43 



Third Group. PERISTOMELLAE. 



The apertiira is oblique without Ivriile, carclelles, or rimule. The 

 ovicell is h.yperstomial and imbedded in the distal zooecia. It opens 

 above (and nearly opposite) the oblique apertura and below the 

 frontal mucro in a locella where the operculum operates. 



The principal genera of this group are listed below with their 

 range; all occur in the North American Eocene and Oligocene. 



Bathosella, new genus. Cretaceous-Midwaj^an. 



Romancheina Jullien, 1888. Jacksonian-Eecent. 



PeHstomella Levinsen, 1902. Lutecian-Eecent. 



ExocheUa Jullien, 1888. Eocanean-Recent. 



Didymosella, new genus. Vicksburgian-Eecent. 



BATHOSELLA, new genus. 



{Bathos, depth.) 



The apertura is oblique, without lyrule, cardelles, or rimule. The 

 ovicell is embedded in the distal zooecia. It opens above the aper- 

 tura and below the frontal mucron in the locella. The frontal is a 

 thick olocyst, more or less covered by a pleurocyst. The zooecia are 

 indistinct. The avicularia are simple and irregularly placed. The 

 areolae are very rare. No spines. 



Genotype. — Bathosella {Mucronella) aspera Ulrich, 1901. 



Range. — Uppermost Cretaceous, Midwayan. 



DIDYMOSELLA, new genus. 



{Didymos, double, having reference to the two large frontal pores.) 



The frontal is a tremocyst. Below the apertura there are two 

 large pores which open into the zooecia under the operculum. Spines. 

 There is a large marginal avicularium, triangular, with pivot, ar- 

 ranged transversally. 



Genotype. — Didymosella (Porma) larvalis MacGillivray, 1868. 



Range. — Vicksburgian-Eecent. 



DIDYMOSELLA CRASSA. new species. 



Plate 4, fig. 6. 

 Description. — The zoarium is unilamellar and very thick ; it creeps 

 over algae. The zooecia are elongated, distinct, in the form of a 

 bottle; the frontal is convex and formed of a tremocyst with large, 

 crowded tubular pores. The apertura is elliptical and transverse; 

 the salient peristome bears the traces of very small spines; two 

 enormous pores are adjacent to the peristome. The avicularium is 

 marginal, triangular, very large, with pivot, and arranged trans- 



