398 BULLETIN 106, UNITED STATES NATIONAL MUSEUM. 



because he must draw on his personal experience for the positive elements of appre- 

 ciation. 



Affinities. The species differs from Plippodiplosia magniporosa, in which the 

 zoarium is also unilamellar, in the greater length of its apertura and zooecium. 

 chiefly in the presence of the median peristomial avicularium. 



Occurrence.- Vicksburgian (Marianna limestone) : West bank of Conecuh 

 Eiver, Escambia County, Alabama (very rare) ; Murder Creek, east of Castlebury, 

 Conecuh County, Alabama (rare) ; near Claiborne. Monroe County, Alabama (rare). 



Vicksburgian (Byram marl) : Byram, Mississippi (very rare) ; Vicksburg. 

 Mississippi (rare in the upper beds). 



C'otypes.Cai. Nos. 64280, 64281, TJ.S.N.M. 



Genus HIPPOZEUGOSELLA Canu and Bassler, 1917. 



1917. Hippozeugosella CANU and BASSLEE, Synopsis of American Early Tertiary Cheilostome 

 Bryozoa, Bulletin 96, United States National Museum, p. 42. 



The ovicell is hyperstomial, its orifice is large, without rapport w-ith the oper- 

 culum, and is closed by a special membrane. The- aperture is elliptical ; two small 

 cardelles separate the anter from the somewhat smaller poster. The frontal is a 

 tremocyst with small pores. The zoarium is free; the zooecia are joined two by 

 two. No spines. Avicularia present. 



Genotype. Hippozeugosella (Bactridium) hagenowi Reuss, 1847. 



Range. Priabonian-Miocene. 



The only species known are Bactridium hagenowi Reuss, 1847, of the Priabonian 

 and Cucullipora tetrasticha MacGillivray, 1895, from the Miocene. 



This genus embraces the two ancient genera Bactridium Reuss. 1869, and 

 Cucullipora MacGillivray, 1895, with limits still more extended. 



Bactridium was created in 1847 by Reuss with unilamellar and biserial species. 

 The first three species belong to Scrupocellaria. Again, in 1869, he maintained his 

 genus, but with Bactridium hagenowi Reuss, 1847, as a type and with a definition 

 based upon the zoarium. In 1891, Waters in studying this species discovered that 

 it had a schizoporellidan aperture. It is very difficult to establish the limits be- 

 tween the schizoporellidan and hippoporinan apertures in the fossil forms. 



The genus Cucullipora MacGillivray, 1895, embraces the bilamellar and biserial 

 species in which the orifice is provided with labial processes. The inconstance of 

 the latter does not permit them to be considered as generic characters. They occur 

 in other genera, such as Watersipora, Lagenipora, etc. 



In the American Tertiary we have one unilamellar, biserial species. Five 

 other species are bilamellar and biserial ; the edge of the two lamellae is visible 

 laterally with a very characteristic aspect. This edge is hidden in a single species 

 (Hippozeugosella scxordinata) by the addition of two supplementary rows. In 

 all these species the mode of ramification is identical. Each new branch is formed 

 by the union of two zooecia arising from two consecutive zooecia (pi. 53, fig. 4). 

 Finally, the mode of gemmation and of the pairing of zooecia reminds one of 

 Catenicella Audouin, 1826, Ichthyaria Busk, 1884. and Urccolipora MacGillivray, 



