NORTH AMERICAN EARLY TERTIARY BRYOZOA. 385 



of the ovicell, in its convex anter and in the absence of the large vibraculum which 

 according to Waters develops at the side of the aperture in the European species. 



The ovicell of this species is very characteristic, but unfortunately it is very 

 rare; in its absence the determination offers some difficulties. It resembles con- 

 siderably HippomcneUa rotula, but differs in the larger aperture (Aa=0.20mm. 

 instead of 0.15 mm. exteriorly) and in the small avicularium placed much lower. 



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

 River, Escambia County. Alabama (common) ; Salt Mountain, 5 miles south of 

 Jackson, Alabama (common) ; Murder Creek, east of Castlebury, Conecuh County, 

 Alabama (common) ; near Claiborne, Monroe County, Alabama (common) ; deep 

 well, Escambia County, Alabama. 



C'otypes.Cat. Nos. 64267, 64268, U.S.N.M. 



HIPPOMENELLA COSTULATA, new species. 



Plate 86, figs. 14-19. 



Description. The zoarium is free, more or less cylindrical, most often com- 

 posed of six longitudinal rows of zooecia. The zooecia are elongated, distinct, oval, 

 separated by a furrow ; the frontal is very convex, finely granulated, surrounded by 

 a single line of small triangular areolae, separated by some short, interareolar 

 costules. The aperture is little elongated and suborbicular in the interior; on 

 the exterior it shows a proximal lip more or less convex and salient ; the peristome 

 bears 4 to 6 spines. The ovicell is hyperstomial, much imbedded in the distal 

 zooecia, garnished with two perforated areas with a large pore and radial costules. 

 The avicularia placed on each side of the aperture are disposed obliquely or trans- 

 versally; they are prominent, subtriangular, and are provided with a pivot. 



Measurements. Aperture [Aa=0.15 mm. . \Lz -=0.65-0. 75 mm. 



Zooecia 



(exterior) I 7a=0.15 mm. lfe=0.40-0.45 mm. 



Variations. The two large pores of the ovicell are often divided into two 

 parts by a small tongue or by an internal crossbar (fig. 17) : the costules are some- 

 times altered (figs. 18. 19). The proximal lip of the aperture becomes sometimes 

 a veritable mucro (fig. 19). The interareolar costules are attenuated (figs. 15, 16) 

 or very complete (fig. 18). The avicularia are constant and symmetrical. The 

 zoarium may have more than six rows of zooecia (fig. 19) and even be incrusting. 



Affinities. In its ovicell this species approaches Hippomenella capitimortis ; 

 it differs from it in the presence of the costules on the ovicell, the greater length 

 of the avicularia and their lateral place on the side of the aperture, and the pres- 

 ence of a single row of areolae (instead of two). 



It differs from Hippomenella rotula in its nonlamelliform zoarium. its some- 

 what larger oral dimensions, the finer costules of its ovicell, and the presence of 

 spines. 



It differs from Hippomenclla angustacdes in its transversal or very oblique 

 avicularia (and not almost longitudinal), in their symmetry and a single row of 

 areolae. 



5589919 Bull. 106 25 



