THE MORPHOLOGY OF THE CHEILOSTOMATA. 345 



round tlie proximal and lateral borders of the frontal sliield, wliicli extends as 

 two wing-like i)rocesses (/. sh. d.) along the borders of the orifice. Each of 

 these processes bears a lateral oral aviculariuni (avic). The calcareous floor of 

 each areola is perforated by a pore throuuh which a strand of living tissue (.r) 

 passes to join a sheet of similar tissue which overlies the froutal shield. The 

 frontal membrane lies at a much lower level than the frontal shield (cf. Fig. 12), 

 and the orifice is not represented. — North Sea. 



Fig. 11. — Umbonua verrucosa, Esper. Young zocecium. The frontal 

 shield is represented by a crescentic calcareous IJlm, already divided by radiat- 

 ing buttresses on its upper surface into distinct areolae («/".), in the floor of each 

 of which is a pore (/;.). The distal wings (/. sA. d.) of tiie shield are distinctly 

 indicated. The parietal muscles {p.m.) are seen through the calcareous film. — 

 Plymouth. 



ElG. 12, — Diagrammatic longitudinal bisection of an Umbonuloid Cheilo- 

 stome. 



Figs. 13 — 17- — Euthyroides episcopalis, Busk. — Victoria. 



Fig. 13. — Young zocecium. The limit of calcification is the line x, 

 distal to which is an accumulation of nuclei {c. s.), to which the parietal 

 muscles (p. m.) radiate. The distal wall {d. w.) of the zooec;ium is not 

 completely calctfied ; e., growing edge of zoarium. 



Fig. 14. — An older but much shorter zocecium, in which calcification 

 is nearly complete. The median pore is becoming delimited by the 

 simultaneous growth of the median tongue {tff.) of calcareous matter and 

 the lateral processes {J.}).). The parietal muscles (;;. m.) radiate towards 

 a mass of tissue at the base of the oiierculum ; c.p., communication pores. 

 Fig. 15. — Older zorecium, with completely calcified walls. The com- 

 pensation-sac {c. s.) now possesses a distinct caviiy, but is still of small 

 extent. 



Fig. IG.— Mature ovicell, borne by a fertile zocecium which has an 

 ordinary zocecium on its proximal side. 



Fig. 17. — A fertile zocecium with a young ovicell {ov.) represented l)y 

 a concave plate, which will constitute the inner wall {i. to.) of the ovicell, 

 and by a second ()lale, which will form the ouier wall (o. w.). The 

 Cribrilina-like frontal bars {/. b.) differ from lliose shown in Fig. 16 

 in correlation with the presence of an ovicell {ov.') on the proximal side of 

 this zocecium. On the distal side of the young ovicell {ov.) is a still 

 younger fertile zocecium whose frontal bars are only half developed. 



PLATE IG. 



Figs. 18 — 31. — Euthyris clatlirata, n. sp. — Fort Jackson. 

 Fig. IS. — Ends of several branches, X 1. 



