22 BULLETIN 9G, UNITED STATES NATIONAL MUSEUM. 



Genotype. — Stamenocella mediaviculifera^ new species. 



Range. — Senonian-Viclcsbiirgiun. 



The genus which is nearest to this type of structure is Bactrellaria 

 Marsson, 1887, in which the zooecia are identical, but are disposed on 

 a single side of a triserial zoarium. The two genera undoubtedly 

 belong to the same family. 



STAMENOCELLA MEDIA VICULIFERA, new species. 



Plate 3, fig. 1. 



Description. — The zoarium is bilamellar, Avith the two lamellae 

 back to back and inseparable. The zoa3cia are very elongated, nar- 

 rowed behind, distinct or indistinct; the mural rim is thin, salient, 

 somewhat enlarged and attenuated, rounded, smooth. The opesium 

 is elliptical or oval, entire; the gymnocyst is somewhat convex and 

 nearly as long as the opesium. The avicularium is salient and ])laced 

 in the middle of the gymnocyst. The ovicell is rarely intact. 



A6>=0.40 nun. 



Zo=0.1G mm. 



Measurements. — Opesia 

 Zocecia 



fZs=0.80 mm. 

 Zs=: 0.20-0.24 mm. 



Variations and affinities. — This species apparently lived in agitated 

 waters. Although widely distributed, it is often very rare, and 

 specimens are always more or less worn. In this condition the mural 

 rim is worn away and invisible, the zooecia indistinct, and the avi- 

 cularia absent or replaced by a concave cicatrix. We have never 

 found the ovicell intact ; it is always more or less broken but its place 

 is clearly visible on the gymnocyst. The avicularium is of the sim- 

 13le type without denticles or pivot. 



Occurrence. — Middle Jacksonian: Rich Hill, Crawford County, 

 and other localities in Georgia (very common). 



Type.—Q^'^i. No. G2581, U.S.N.M. 



Family AETEIDAE Smitt, 1867.. 



Zoarium composed of creeping branches more or less adherent to 

 the substratum, often growing in free tufts adherent only part of 

 their length. Zooecia uniserial, arising from each other in a tubular 

 prolongation of greater or less length. Opesium terminal, opercular 

 valve at its summit. (After Robertson.) 



Genus AETEA Lamouroux, 1812. 



The American Eocene deposits contain two species of this genus 

 which for lack of well-preserved specimens can only be referred to 

 the well-known recent species Aetea anguina Linnaeus, 1758 and A. 

 truncata Landsborough, 1852. 



