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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 



D -25 H 40 I ' 



FIG. 86. Genus Arachnopusia Jullien, 1SS6. 



A-J. Arachnopusia monoceros Busk, 1854. A, B. Zooecium and one of the large marginal 

 uvk-ularia. (After Hincks, 1881.) C. Young cells. (After Hincks, 1884.) D. Zooecia, X 

 !'.:>. E. Orifice of zooecium, X 50. F. Immersed aviculariuni, 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 zooeeia 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, 1886.) I. Ancestruhi, X 70, with a young zooecium with five spines. (After 

 Jullien, 1886.) J. Growing ends, X 25, showing the calcareous projections n rising from the 

 side, thus forming pores. In the left-hand zooecium (a) the lower calcareous wall below the 

 <>r:il 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 aud has made a semicircular growth. Be- 

 tween the zooecium a and 6 there was another, but this has been omitted. (After Waters. 1906.) 



a concave poster without carclelles; 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 aviculariuni 

 is placed near the aperture. 



