252 



ture. The poster of Ihc aperture is Irilohcd, while its anter, which is surrounded 

 ])y a strongly protruding, not bilohate margin, has two proximally converging 

 lateral margins. 



The lateral chambers, hi every internode llie scapular eliamher generally 

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

 two daughter-zod'cia, whereas no other avicularia occur. The correspoudiug sujjra- 

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

 which is hut incompletely seiiaraled from the cavity occujiying the remaining 

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

 sion on the outside of each daughter-zocrcium. To understand the form and ex- 

 tension of the other chambers we must lirst study the system of jirojecting ridges, 

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

 (lig. lie) we see, thai 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 

 zoa'cium to the annular facette of the joint and is continued from the basal side 

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

 the distal surface a continuous transverse ridge may ap[)ear, situated vertically 

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

 the centre of the apertures of the two lateral zou'cia, but in many cases we tind 

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

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

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

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

 transversely situated, deep pit with (5—8 pores. On the frontal side of these, two 

 long, |)ointed cavities are seen between the three zoojcial apertures (fig. 11a), 

 each commuuicating through a [\\[ with 1— ;$ pores sometimes with the daughter- 

 zoG'cium, sometimes through a corresponding pit with the mother-zoa'cium as 

 well. Considering the two daugbter-zoa-cia as the scajiular 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 re])re.senling the supra-scapular 

 chambers of the mother-zoa-cium. From Ihe |)ro\iuud 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 (lig. lid), namely, opposite the nu'dian fenestra, and terminates 

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

 partly by this ridge, partly by the median ridge and by Ibe nuugin of the 

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

 nniltij)orous rosette-plate (tig. lid, d. 1\'). The distal of the two lateral ridges. 



