. . , bRYOZOA. 153 



Paohydictya.] 



vals ; angle of bifurcation unusually wide. Non-poriferous margin very wide, 

 extremely thin and sharp, and wavy or ruflfled ; its surface is obliquely striated, 

 the striae really rows of minute hollow papillae, which communicate with the hori- 

 zontal median tubuli between the mesial laminae. Zocecia in from seven to twelve 

 ranges, the usual number ten or eleven ; their apertures elliptical, usually a little 

 wider than the transverse interspaces, and longer than the end spaces. In the five, 

 six, or seven central rows the apertures are arranged in regular alternating or sub- 

 alternating longitudinal series, in which thirteen or fourteen occur in 5 mm.; rneas- 

 uring transversely six TOWS take up a space of 1.5 mm. wide. The one to three 

 marginal rows are not so regular in their arrangement, they being, besides, appre- 

 ciably larger and separated by wider interspaces, while their long diameter is, usually 

 at least, directed somewhat obliquely outward. 



On plate IX, fig. 13 represents part of a tangential section, showing, at the top, 

 the primitive or prostrate portion of the zocecia, and mesial laminae with horizontal 

 tubuli ; along the right side, the wide non-celluliferous border, which in thin sections 

 is irregularly outlined and incomplete, because of its "ruffled" character ; and in the 

 lower left-hand fourth, the zooecia and interspaces as they appear just beneath the 

 surface. In the last portion of the figure the chief feature to be pointed out is the 

 unusual clearness and thickness of the ring-like zooecial investment. In common with 

 perhaps every species of this section of the genus, and many of section a, the longi- 

 tudinal arrangement of the zooecia between distinct lines, either straight or flexu- 

 ous, and proving on closer inspection to be series of minute pores, prevails in the 

 central rows through all stages, saving, perhaps, the last in very old examples. 



Good examples of this species cannot be confounded with any other known to 

 me, since the great width and wavy or ruffled character of the non-poriferous 

 margin gives them a very striking and highly characteristic aspect. In most other 

 respects the species resembles P. acuta Hall, sp., and its western varieties rather 

 closely. It may be compared also with P. elegans and its described variety. In that 

 species and variety tlie non-poriferous margin is also rather wide, but it is not wavy 

 and the inter-apertural spaces are wider, especially those between the. ends of the 

 zooecial apertures, while the whole surface of the zoarium strikes one as more highly 

 ornamental. Considerable differences are likewise to be noted in tangential sections 

 as may be seen in comparing flguLes 8 and 13 on plate IX. 



Formation and locality.— Rather common in the lower half of the Trenton shales at Minneapolis and 

 St. Paul, Minnesota. It occurs also in the "Pierce " limestone of Tennessee. 



Mus. Beg. Nos. 5950, 5951. 



