BRYOZOA. 285 



Diplotrypa.l 



pores. Zocecial apertures rounded, mostly subcircular, regular, twelve or thirteen 

 in 3 mm. Closures preserved in one out of about forty specimens-, slightly concave, 

 apparently smooth and without a raised rim about the central perforation. Walls 

 of moderate thickness, ridge-shaped. Mesopores numerous, rather small, but dis- 

 tinctly visible under a good pocket lens. 



Internal characters: These are remarkable chiefly in vertical sections, tangential 

 and transverse sections being very much like those of C. pulchella and C. ramosa. 

 In vertical sections namely there seems to be a total absence of diaphragms, not 

 only in the zooecial tubes but in the mesopores as well. Another peculiarity is the 

 crenulated or wavy character of the walls in the axial region that has suggested 

 the specific name. This crenulation is shown very distinctly when the tubes are 

 exposed by vertical fractures. 



The two peculiarities mentioned in the preceding paragraph distinguish the 

 species from all the others now referred to the genus. In other respects we are 

 reminded of its associate C. pulchella, yet they ought in no case to be confounded, 

 since in that species the branches are more slender and do not inosculate, and the 

 zooecial apertures are appreciably smaller. 



Formation and locality. — Not uncommon in the upper third of the Trenton shales at St. Paul and 

 near Cannon Falls, Minnesota. Rare In the Galena shales (here almost invariably without monticules) 

 at the same localities, and at.Decorah, Iowa, and Neenah, Wisconsin. 



Miis. Beg. ISos. 8019, 8038, 8068, 8082. 



Family DIPLOTRYPIDtE, Ulrich. 

 For remarks on this fSmily see pp. 276 and 290. 



Genus Dl'PLOTRTPA, Nicholson. 



Zoaria massive or discoid, generally free. Zooecial tubes comparatively large, 

 with thin prismatic walls, and horizontal diaphragms. Mesopores few to numerous, 

 varying in size, many of them enlarging gradually and assuming the characters of 

 true zooecia. Acanthopores wanting. 



Type : D. petropolitana Pander, sp. 



The relations of this genus are with Batostoma on the one hand and Monotrypa 

 and Callopora on the other. Species are few and, so far as known, all belong to Lower 

 Silurian rocks. The two about to be described are aberrant in having very few 

 mesopores. 



