488 BULLETIN 106, UNITED STATES NATIONAL MUSEUM. 



PORELLA UNGUICULATA, new species. 



Plate 64, figs. 1-5. 



Description. The zoarium is unilamellar and creeps on algae. The zooecia 

 are distinct, elongated, fusiform: the frontal is convex and is terminated distally by 

 a long ungulate mucro covering the apertura : it is formed of a tremocyst with 

 scattered pores, disposed in quincunx. The apertura is invisible exteriorly ; the 

 peristome is wanting. The ovicell is hardly salient ; the pores of the area are much 

 smaller than those of the frontal: it is hyperstomial and opens into the peristomie. 

 The median avicularium is large, oblique, smooth, totally burying the apertura. 



[7, s =0.72 mm. 

 Measurements. /ooecia , _ 



lfe=0.3i mm. 



Affinities. This species much resembles Porella jacksonica^ of which it is per- 

 haps the creeping form. It differs from it in its smaller tremopores. the exagger- 

 ated length of its median avicularium. which always covers the apertura on the 

 well preserved specimens, and in the absence of all adventitious avicularia. 



In the interior (fig. 5) the olocyst is thick; the proximal border of the apertura 

 is convex; the mucro is visible. 



On the zoarial margins the avicularium is more fragile and more easily broken 

 (% 3). 



Occurrence. Middle Jacksonian ( Castle Hayne limestone) : Wilmington, North 

 Carolina (common). 



Cotypcs.Cnt. No. 64151, U.S.X.M. 



PORELLA PLANULATA, new species. 



Plate 64, figs. 6-9. 



Description. The zoarium is bilamellar and formed of two lamellae, back to 

 back and inseparable. The zooecia are distinct, elongated, rounded in front, nar- 



i-owed behind, separated by n salient thread; the frontal is fat and formed of a 

 tremocyst with large tubules resting on an olocyst with small pores. The apertura 



(in the interior) is formed of a semi lunar anter and of a very concave poster; at 

 the exterior the peristomice is elliptical and the peristome very thin. The median 

 avicularium is very small, buried in the thickness of the tremocyst and opens into 

 the. peristomie; it is visible only by abrasion of the surface. Sometimes avicularian 

 zooecia are intercalated among the normal zooecia. 



rfy;e=0.22 mm. . f 7,2=0.90-1. 10 mm. 



Measurements. Peristomice L 1 Zooecia 7 



\lpe=0.l8 mm. [fc=0.40-0.45 mm. 



Affinities. This grand and beautiful species is remarkable, but we still possess 

 no specimen with an ovicell. The median avicularium is absolutely invisible ex- 

 teriorly: by properly inclining the preparation its orifice is visible: upon abrasion 

 of the surface it appears like a small cavity in the thickness of the tremocyst (fig. 9). 



In the interior certain zooecia are divided in two parts by a partition, of 

 whose use we are absolutely ignorant (fig. 8). 



