«H . n -, BKYOZOA. ]81 



otiotoporella.l 



Between the ends of succeeding zooecial apertures one or two small mesopores. 

 There is usually a row of these small pores along the border of the branches. Inter- 

 spaces narrowly rounded or ridge-shaped, comparatively thin." 



This neat species is near S. interstincta from the Utica horizon of the Hudson 

 River group, but has somewhat narrower branches, fewer mesopores, and much thin- 

 ner walls. In S. annularis the walls are much thicker, branches wider, sloping areas 

 about the zooecial apertures polygonal, and the mesopores less numerous and irregu- 

 larly distributed. S. dumosa has wider and oftener divided branches. 



Formation and locality.— R^k in the lower part of the upper third of the Trenton shales, at St. Paul, 

 Cannon Falls, and near Fountain, Minnesota. ' 



Stiotopobella dumosa n. sp. 



(Not flgared.) 



Zoarium forming bushy masses, as much as 100 mm. in diameter and 50 mm. 

 high, consisting of very irregulfirly divided, free or coalescing, small branches, 1.5 to 

 2.0 mm. in width, and usually less than 0.5 mm. in thickness. Zooecial apertures 

 subcircalar or elliptical, set into rather wide sloping areas of polygonal or rounded 

 outline, the shape depending upon the number of mesopores present. Arrangement 

 rather irregular; occasionally longitudinal rows, with the mesopores between the 

 ends of the zooecial apertures, prevail, in which case the surface appearance is much 

 the same as in S. rigida. More commonly, however, a diagonal arrangement predom- 

 inates, with the mesopores distributed more at random. In these, especially when 

 the mesopores happen to be fewer than usual, the general appearance is much more 

 like that of S. angularis. Where the arrangement is the most regular there are ten 

 or eleven zooecial 'apertures in 3 mm. diagonally, and about eight in the same space 

 longitudinally. Apertures often closed by a slightly convex plate, in which a minute 

 subcentral perforation may be detected. Walls ridge-shaped, generally wider than 

 the diameter of the zooecial apertures. Mesopores varying in number ; sometimes a 

 fragment will show about one only to each zooecium, while others may have them 

 three or four times as numerous. Edges sharp, generally exhibiting two or three 

 rows of mesopores. 



Internal structure, especially in transverse and vertical sections, very similar to 

 that of S. cribrosa. In tangential sections the mesopores are not as distinct, and the 

 divisional line between the zooecia less sharply defined, than in similar sections of 



that species. 



As a rule I do not favor descriptions of species without illustrations, but in this 

 case the form is so easily recognized that the omission may be pardoned. Com- 

 pared with S. angularis it is distinguished by its more irregular and stronger growth. 



