252 



ture. The poster of the aperture is trilobed, while its anter, which is surrounded 

 by a strongly protruding, not bilobate margin, has two proximally converging 

 lateral margins. 



The lateral chambers. In every internode the scapular chamber generally 

 seems to be developed as a small triangular avicularium on the outside of the 

 two daughter-zocecia, whereas no other avicularia occur. The corresponding supra- 

 scapular chamber appears on the distal surface as a small, triangular cavity, 

 which is but incompletely separated from the cavity occupying the remaining 

 part of the distal surface. It is moreover cor^tinued into a long, narrow depres- 

 sion on the outside of each daugliter-zocecium. To understand the form and ex- 

 tension of the other chambers we must first study the system of projecting ridges, 

 which separates them. On regarding a tri-zocecial internode from the distal surface 

 (fig. lie) we see, that the latter is divided into two lateral halves by a longi- 

 tudinal ridge, which passes from the distal margin of the aperture of the central 

 zooecium to the annular facette of the joint and is Qontinued from the basal side 

 of the latter along the centre of the basal surface. Along the frontal margin of 

 the distal surface a continuous transverse ridge may appear, situated vertically 

 on the just-mentioned longitudinal ridge. The transverse ridge may pass beyond 

 the centre of the apertures of the two lateral zooecia, but in many cases we find 

 in its place two shorter or longer separate transverse ridges, which are not joined 

 on to, the longitudinal ridge. The greater part of the distal surface is occupied 

 by two large lateral chambers covered by a membranous roof, which we may 

 for the present term the distal chambers and which are each provided with a 

 transversely situated, deep pit with 6 — 8 pores. On the frontal side of these, two 

 long, pointed cavities are seen between the three zooecial. apertures (fig. 11 a), 

 each communicating through a pit with Ij-S pores sometimes with the daughter- 

 zooecium, sometimes through a corresponding pit with the mother-zocecium as 

 well. Considering the two daughter-zocBcia as the scapular chambers of the 

 mother-zooecium we must regard not only the two distal chambers but also the 

 triangular ones on the frontal side of them as representing the supra-scapular 

 chambers of the mother-zocecium. From the proximal half of the basal, median, 

 longitudinal ridge two curved, more or less strongly ascending ridges start on 

 either side, of which the proximal one forms the boundary of the sternal area 

 for some distance (fig. lid), namely, opposite the median fenestra, and terminates 

 in a small process just proximally to the avicularium. The cavity, bounded 

 partly by this ridge, partly by the median ridge and by the margin of the 

 sternal area, is the pedal chamber and on the frontal surface it has a very deep 

 multiporous rosette-plate (fig. lid, d. IV). The distal of the two lateral ridges. 



