148 



meus of Bntostoma varians and B. Prosscri. They are also typically de- 

 veloped in the following genera of the Trepostomata : Bythopora, Callo- 

 pora, Dekayia, Eridotrypa, Monticulipora, Nicholsonella and Peronopora. 

 It seems quite probable that communication pores are characteristic of all 

 of the Trepostomata. They are most numerous near the surface, but are 

 sometimes found in the deeper portion of the mature region. They are 

 most readily seen in fairly thick tangential sections cut near the surface 

 of well preser^-ed material ; but very thin sections show their structure 

 better. Communication pores may also be seen occasionally in longitudi- 

 nal sections. These pores usually pass through the region where the inter- 

 zooecial wall is narrow, going directly from one zooecium to another. But 

 (hey are sometimes very irregular in their course. They may be straight, 

 curved, or looped, and are sometimes branched, so as to connect thresh 

 zooecia. In the sections the pores usually appear clear and empty, but 

 they sometimes are filled with dark colored, opaque pellets. 



Batostoma varkibUe was quite certainly derived from B. minneso- 

 tcnse Ulrich, of the middle Trenton formation of Minnesota' ; from which 

 locality it migrated southward during the late Richmond invasion. The 

 two species seem to be almost identical. 



B. prosacri, in everything but the possession of imperfect diaphragms, 

 presents striking points of resemblance to Hcmiphragma irrasum Ulrich.' 

 In B. proftscri, however, the diaphragms are always complete, so that it is 

 a true Batostoma. 



Batostoma varians api)ears to be more closely related to the Edeii 

 forms, B. jamesi (Nicliolson) and B. imjHicatiDii. The detailed description 

 of these three Richmond species follows. 



Batostoma varians (James). 



Plate I. Figs. 1-le ; Plate VII, Figs. .3, 3a. 



ChcEtetcs rar'Mns. James, Taleontologist, No. 1, 1878, p. 2 (not figured). 

 Monticulipora (Chdtetes) varians. James, Paleontologist, No. 5, 1881, p. 



36. 

 Monticulipora varians. James and James, Jour. Cin. Soc. Nat. Hist., Vol. 



X, 18S8, p. 177, pi. ii, Figs. 4a, 4b. 



' Geology of Minnesota, vol. iil, pt. i, p. 297, pi. 2G, figs. 38-40 ; pi. 27, 

 figs. 0-15. 



2 Ibid., p. 299, pi. xxiv, figs. 5-9. 



