MARVT.AXT) f;i:or.f)(;i( \i. >ri;\ i;\- 231 



or less irregularly in curved series. Unc oi' six in ".' nmi. often separated 

 l)y a dc|)i'('ssc(l line. I'lunl wall |)iiii(lalc. sligiilly convex, flat, or de- 

 pressed, the la>l when the iiiai-<;iu on one or l)oth sides is thickened and 

 elevated. A|iertuic snli(|iia(li'ate or seniirlli|)tical, sometimes contracted 

 near (lie niidille. always ciicloseil liy a more or less stroni^'ly tliiekeneil 

 ]'ini. A\icnlaria oceui- on llie I'aised apeil iii'al lioi'iicr, usually one to 

 eaeli zooi'cinin. oi' two. as shown in the ligiii-es on i'late LXI. Ooecia 

 iniknow n. 



Orcurreiicf. — A(,)riA I''()i;m A'l'iox. Tapper Marlboro. 



Culled ion. — ]\rarylan(l (ieologieal Survey. 



Genus MUCRONELLA Hincks. 

 MUCROXELLA ASPERA n. Sp. 



Plate LX, Figs. 17, 18. 



Description. — Zoarium incrusting, consisting of one or more layers; 

 surface under a low power of magnification presenting a decidedly 

 rough aspect. Zooecia varying from ovate-hexagonal, to suh-rhomboidal, 

 indistinct externally, arranged more or less irregularly, though the rows 

 are more regular than they may appear at first sight; about six in 2 

 mm. Apertures rounded or suhquadrate, 0.13 mm. in diameter, ren- 

 dered oblique by the elevation of the more or less strongly swollen pos- 

 terior margin and the depression of the anterior part. The central por- 

 tion of the raised lip forms a " mucro '" of greater or less thickness and 

 prominence, the same hiding a minute central tooth beneath it, and 

 forming with the rest of the thickened portion of the lip, a more or less 

 obscure resemblance to the figure AV. Behind the lip the surface slopes 

 rapidly and in the most nearly joerfect example is granulose. In the 

 depressed space in front of the aperture there are, normally, three 

 small raised avicularia ( ? vibracula) while a few larger avicnlaria, dif- 

 fering further from the others in being divided into two unequal parts 

 by a cross-bar, are scattered without order among the zooecia. Ooecia 

 are not often seen. AYlien present, they occupy the depressed space 

 in front of the aperture, are cucuUate, abont as large as the zooecial 

 aperture, and usually bear a furrow running from the summit to the 

 concave edge. 



