THE MORPHOLOGY OF THE CHETLOSTOMATA. 277 



That of the operculum is so close to the insertion of the 

 buttress into the vertical distal wall as to receive support 

 from the buttress. That of the "lower jaw" is continuous 

 with the main thickening- of the labium, which is the deeper 

 wall, as shown in fig. 26. 



I have few observations on other points in the structure of 

 this species. In the material at my disposal a certain 

 amount of disintegration appears to have taken place before 

 the specimens were preserved. 1'lie number of tentacles is, 

 however, about twenty-two. 



Euthyris obtecta, Hincks/ PI. 16, figs. 32 — 37. 



The B-zooecia are much larger than the A-zooecia, the 

 ratio in volume being probably at least 2 : 1 (figs. 32, 35). 

 'J'he A-opercula are of much the same shape as in 

 E. clathrata, while the B-opercula are relatively much 

 broader. The condyles are weaker than in E. clathrata, 

 and are situated nearer the proximal border of the oper- 

 culum. But what most strikingly differentiates the two 

 species is the character of the calcification. The calcareous 

 wall is everywhere complete in E. obtecta, the basal wall 

 being uniformly rounded along its whole extent. Both kinds 

 of zooecia are flask-shaped (figs. 34, 36), the opening* of the 

 neck of the flask being filled by the operculum. A con- 

 tinuous flat epitheca overspreads the entire zoarium, being 

 stretched out in the plane of the opercula on the frontal 

 surface of the branch, and at a considerable distance from 

 the zocecia on the basal surface (fig. 34, ejp., b. ep.). The 

 space beneath the epitheca (ep. c.) is thus extremely large, 

 and that of the frontal surface is continuous with that of the 

 opposite side by means of the undivided space which runs 

 along each edge of the frond (figs. 32, 35, tn. c). 



On the frontal surface the epitheca is supported in the 



main by the edges of the orifices of the zooecia, but in 



addition by a few calcareous tubercles (fig. 34, calc. j^-), 



which arise irregularly from various points of the surface of 



' ' Ann. Mag. Nat. Hist.' (5), x, p. Ifii ; (G), xi, p. 177. 



