498 PALAEONTOLOGY OF ILLINOIS. 



DICHOTRYPA Ulrich. 



(For generic diagnosis see page 386.) 



Only one previously described species, the Fistulipora, flabel- 

 luw, of Rominger, seems to have the characters ascribed to this 

 genus, yet I do not doubt that when the Palaeozoic Bryozoa 

 are more fully worked out, the genus will occupy a prominent 

 place in our classification. Already I can determine seven well 

 marked species, beside fragments of one or two other species 

 from the Keokuk group. The seven described here belong, one 

 to the Niagara, one to the Hamilton, and five to the St. Louis 

 group. The great prominence of the genus in the last forma- 

 tion is a rather peculiar circumstance, since remains of Bryozoa 

 are comparatively rare in these beds. 



DICHOTRYPA GRANDIS Ulrich. 



PI. XLII, Fig. 1-le. 



Zoarium a large undulating frond, attaining a height of 13 

 cm. or more, a width of more than 7 cm., and at hickness of 4 

 or 5 mm. Surface smooth, but exhibiting, generally, small and 

 inconspicuous solid maculae. Apertures arranged in bent 

 diagonal series, about seven in three mm. measuring longitudi- 

 nally or diagonally, with a total absence of ridges, the inter- 

 spaces being flat. Orifices sub-oval, about 0.15 mm. in diame- 

 ter, with slightly elevated peristome. Interspaces from one and 

 a half to twice the diameter of the apertures. Zotecia at first 

 thin-walled, prostrate, commonly of obovate form; with the 

 vestibule tubular and traversing the space to the surface at a 

 right angle with same. Interspaces filled with vesicles, which at 

 first decrease in size outward, and, long before the surface is 

 reached, become filled with solid tissue. Lunarium occupying 

 from one-third to one-half the circumference of the zo<Bcial 

 boundary, not very conspicuous, but usually with one end pro- 

 jecting tooth-like into the cavity. 



This is the strongest as well as the earliest species of the 

 genus known. In its minute structure it seems to compare more 



