BKYOZOA. 241 



Homotrypa tuberoulata.] 



Zoarium small, ramose, branches rounded or flattened, dividing rather fre- 

 quently, 2.0 to 3.5 mm. thick, and 2.5 to 7.0 mm. wide. Surface more or less 

 strongly tuberculated, the monticules 2 to 2.5 mm. apart, conical, often very prom- 

 inent. Zooecial apertures nearly fourteen in 3 mm., angular or rounded, more or 

 less oblique except in the oldest examples, in most specimens exposing the cysti- 

 phragms. Walls thin, often separating so as to form considerable interspaces in 

 which a greater or less number of closed mesopores is contained. The extent of 

 these interspiaces varies greatly, being sufficient in some instances to cause the 

 zocecial apertures to be of w)unded or ovate form, while in other specimens they are 

 scarcely appreciable. Acanthopores small, about one to each zooecium. 



Internal characters: In verticatl sections the tubes are large and without dia- 

 phragms in the axial region, the latter, together with short and rather irregular 

 series of cystiphragms, being developed in the narrow peripheral region only. 

 The mesopores appear as shown in the figure. Of tangential sections it would be pos- 

 sible to select small portions differing so much from each other in the number of 

 mesopores that they would scarcely be suspected of belonging to one species. Still, 

 if the sections are large enough each will contain some parts that may be said to be 

 practically the same as those represented in figs, c and d. The acanthopores, though 

 small and few, are quite distinct in these sections. 



This is another of those aberrant forms of the genus like H. mtercalaris. While 

 its relations seem often to be decidedly suggestive of Homotrypella (?) ovata, I do not 

 believe that its development resulted in that form. It seems to be an offshoot, per- 

 haps from that line, which'latter produced the H. obliqua Ulrich, of the Cincinnati 



group. 



The strong monticules distinguish the species from the Trenton forms of the 

 genus. Associated with it there are two really very distinct though dangerously 

 similar species. The first of these is the Ataotoporella ramosa with ite numerous 

 acanthopores and infiected zooecial apertures, and totally different internal struc- 

 ture. The second, Callopora persimilis, differs so widely in its internal structure 

 that it will be sufficient to refer the student to the figures on plate XXII. Other 

 species presenting more or less superficial resemblance might be mentioned, but I 

 cannot regard it as necessary, since with the aid of thin sections the student will 

 have no trouble in distinguishing them. 



Formation and ZocaZ^.-Upper third of the Trenton shales, near Cannon Falls, Minnesota. The 

 species probably occurs in the same beds at St. Paul. 

 Mus. Beg. No. 8123. 



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