BRYOZOA. 335 



slender spindle-shaped, united to each other by their extremely 

 attenuated terminations, or by an uninflated filiform tube. The 

 substance of the zoarium is very thin, dark brown or black, 

 and only rarely preserved, but on account of its curious habit 

 of excavating the substance of the body upon which it grew, 

 the form of the zoarium, as well as that of the zocecia is gen- 

 erally clearly defined and recognizable. The orifice is small, in- 

 distinct, and readily overlooked in the best specimens at hand. 

 Khopalonaria compares favorably with species of Arachni- 

 diuni Hincks; A. clavatum Hincks (loc. cit. pi. 71, figs. 3,4,5) 

 is especially recommended. 



The species of Ascodictyon and Rhopalonaria should perhaps 

 be placed in distinct families, but, as it is not probable that 

 either one of the genera belongs to any of the recent families, 

 and as our opportunities for comparison between fossil forms of 

 the suborder are necessarily very limited and unsatisfactory, I 

 regard it sufficient for present needs to arrange the Palaeozoic 

 species in one family, the ASCODICTYONID^E. 



II. Cyclostomata. The forms of this suborder are character- 

 ized throughout by simplicity of structure, the zocecia being 

 always tubular, with the mouths simple, rounded, inoperculate, 

 and generally exert; the walls thin, of nearly uniform thickness 

 throughout, and minutely perforate; all appendicular organs 

 are wanting. The polypide also is more than usually simple in 

 structure, has comparatively a small number of tentacles, while 

 the larva? of the principal families are almost identical. It is 

 really a very difficult matter to divide this suborder into satis- 

 factory families and genera. On account of the extreme sim- 

 plicity and uniformity of the zooecium, we must depend almost 

 entirely upon variations in zoarial habit and mode of zooecial 

 aggregations. These are generally striking, and among Palaeo- 

 zoic forms at any rate, usually reliably indicative of true rela- 

 tionship. Thus, while in Mitoclema the zooecial tubes are long 

 and radiate equally in all directions to open on all sides of a 

 cylindrical stem, they are shorter, beaded proximally, and those 

 opening on each side of the compressed branches, are separated 

 by an axial plane in Diploclema. Protocrisina again differs 

 from both in having one side of the branches without cell aper- 

 tures. 



