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BULLETIN 106, UNITED STATES NATIONAL MUSEUM. 
the frontal is convex, formed of calcareous polygonal pieces perforated by a large 
pore; each pore is semilunate and has an interior denticle; the convex side of this 
pore is turned toward the exterior, but the denticle is directed toward the zooecial 
axis; the cribriform area is surrounded by a smooth collar, composed of adjacent 
polygonal pieces. The aperture is elongated and formed of a semilunar anter and 
Fig. 86. — Genus Arachnopusia Jullien, 1886. 
A-J. Arachnopusia monoceros Busk, 1854. A, B. Zooecium and one of tlie large marginal 
avicularia. (After Hincks, 1881.) C. Young cells. (After Hincks, 1884.) D. Zooecia, X 
25. E. Orifice of zooecium, X 50. F. Immersed avicularium, X 50. (D--F after Busk, 1884.) 
G. Avicularian mandible, X 85. (After Waters, 1887.) 
H. Young zooecia, X 40, bearing two or three marginal spines. There are other colonies 
of zooecia which have four of them. These marginal spines disappear promptly, except that 
one which is nearest the posterior lip of the orifice, and whose base alone persists ; it is from 
the base of the spine that the species derives its name. The avicularian cavity forms here in 
great relief, and its circumference must soon increase on account of the calcareous deposit. 
(After Jullien, 1S86.) I. Ancestrula, X 70, with a young zooecium with five spines. (After 
Jullien, 1886.) J. Growing ends, X 25, showing the calcareous projections arising from the 
side, thus forming pores. In the left-hand zooecium (a) the lower calcareous wall below the 
oral aperture is not complete. Above the zooecia (distally) the basal and lateral walls are found 
before there is any other sign of growth, and in the division thus formed above the right-hand 
zooecium the calcareous front wall is commencing and has made a semicircular growth. Be- 
tween the zooecium a and b there was another, but this has been omitted. (After Waters, 1906.) 
a concave poster without cardelles; the peristome is salient, smooth, and bears a 
distal lip, very prominent and oblique, and an acute, proximal mucro. The ovicell 
is hyperstomial, opening in the peristomie above the operculum; its ooecial cover 
is formed of various rectangular, calcareous pieces. A large elliptical avicularium 
is placed near the aperture. 
