^BT. 2] CYCLOSTOMATOUS BRYOZOA CANU AND BASSLEK 89 



SIPHODICTYUM IRREGULAHE, new species 



Plate 14, figs. 1-11 



Description. — The zoarium is cylindrical, slender, dichotomously 

 branched. On the cellular face the orifices are arranged in irregular 

 quincunx or in transverse lines interrupted in the middle; the peri- 

 stomes are salient, thick, adjacent, or scattered; they are separated 

 by groups of 2 to 4 vacuoles. On the dorsal face the vacuoles occur 

 at the base of sulci of little depth, arranged longitudinally and 

 obliquely. At the extremity of the branches the peristomes occur 

 entirely around the colony. The cellular groups are separated by 

 noncellular spaces showing only vacuoles. The ovicell is a large, 

 very convex sack placed in the noncellular portion of the zoarium. 



Measurements. — Diameter of orifice, 0.08 mm.; zooecial diameter, 

 0.12 mm.; distance of orifices, 0.28-0.32 mm.; diameter of largest 

 branches, 0.65 mm. 



Structure. — The longitudnial section of the cellular branches shows 

 on the frontal a thick peripheral epitheca perforated by vacuoles, 

 short cylindrical tubes with triparietal gemmation around a central 

 axis, and dorsal tubes analogous but aborted and engendering the 

 vacuoles. 



The longitudinal section of the noncellular branches show identi- 

 cal characters, but all the tubes arc aborted and engender numerous 

 vacuoles. 



The transverse section shows a very thick epitheca perforated by 

 vacuoles, by complete tubes, or by incomplete tubes. 



The tangential section of the cellular face shows the orbicular 

 orifices and a variable number of small vacuoles very irregularly 

 arranged and immersed in a thick epitheca. Irregular veinules indi- 

 cate the presence of the sulci. The tangential section of the non- 

 cellular portions exhibit very small vacuoles arranged in quincunx 

 and immersed in a thick epitheca in which the veinules are indicated 

 by the darker portions. 



This species has afforded sections closer to those of Gregory, 1899 

 (p. 364) ; but the walls of the adventitious tubes are much thicker 

 and seem to indicate vacuoles rather than mesopores. 



The orifices are arranged in transverse rows, interrupted or in quin- 

 cunx. On the same zoarium there are large cellular spaces with peri- 

 stomes on a snigle side, but they alternate with the large noncellular 

 spaces. At the extremity of the branches the orifices are disposed 

 entirely around the colony. The lateral dichotomisations are always 

 very short. 



