American Palaeozoic Bryozoa. 



173 



able to ascertain, are sufficiently distinct from those of typical species 

 of Ptilodictya to permit a generic separation. I do not know that any 

 specimens of P. constellata have been discovered which preserved the 

 basal extremity: but judging from the general characters of the zoari- 

 um and its cellular structure, I am inclined to believe that the species 

 possessed an articulating process or head, similar to that which char- 

 acterizes Ptilodictya. The description of Phaznopora explanata im- 

 mediately follows that of the genus, and this species must therefore be 

 regarded as the type of the genus. Through the courtesy of Prof. R. P. 

 "Whitfield, of the Amer. M" us. of Nat. Hist., New York City, I was per- 

 mitted to see the specimens upon which this species was founded. 

 These are, however, but poorly-preserved fragments, that do not pre- ' 

 serve the basal portion of the zoarium, and, in consequence, I am un- 

 able to decide, with any degree of certainty, whether Phaznopora should 

 be classed with the Ptilodictyonidce or the Stictoporidai. My only 

 reason for placing the genus with the latter family is found in the fact 

 that P. (?) multipora belongs there. That this species is congeneric 

 with P. explanata is doubtful, and must remain so until good speci- 

 mens of the type species can be subjected to microscopical examination. 



Formation and locality: P. (?) multipora is not an uncommon fos- 

 sil in the upper beds of the Trenton group, at Burgin, Ky. 



Pachydictya, robusta, nov. gen. et. sp. (PI. VIII., figs. 10, 10a, 106, 



and 10c.) 



Pachydictya, gen. char., ante p. 152. 



Zoarium robust, ramose, branching at intervals, varying from .3 inch 

 to one inch. Branches varying in width from .2 inch, to over .5 inch, 

 and in thickness from .05 inch to .15 inch. No n -poriferous margin 

 usually well-developed, smooth. Cell-apertures comparatively large, 

 oval to sub-circular, and arranged in more or less regular series; about 

 six occupy the space of .1 inch. The interstitial cells usually can not 

 be detected at the surface, and when most distinct they appear as only 

 shallow elongated pits occupying the summits of the moderately thick 

 cell-walls. At irregular intervals they are gathered into unequal 

 "maculae," which may be level with the general surface, or elevated 

 into small monticules, and either smooth and apparently solid, or 

 minutely punctate. When mature, the interstitial cells appear to have 

 been covered by a minutely poriferous interstitial membrane. 



In longitudinal sections the tubes arise very abruptly from the me- 

 dian axis, near which their walls are very thin; as they proceed toward 



