148 



iiUMjs of liittdsldiint raikins iuid /?. /'rossrri. They are also typically de- 

 veloped in tiie followiiii? ,i,'enera of the Trepostomata : Bi/tlioitora, Callo- 

 pora, Dvkayla, Eridotnjpa. MoiiticuliiKtra, Nicholsonclla and I'cronopora. 

 It seems quite probahle 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 presex-ved material ; hut 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 

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

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

 zooecia. In the sections the poi'es usually appear clear and empty, but 

 they sometimes are filled with dark colored, opaque pellets. 



Batostoma variubUe was quite certainly derived from B. mimieso- 

 tense 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. prossvri, in everything but the possession of imperfect diaphragms, 

 presents striking points of resemblance to Hcmlpliragma irrasum Ulrich."- 

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

 a true Batostoma. 



Batostoma rarians api)eai's to be more closely related to the Edeb 

 forms, B. jautcsi (Nicholson) and B. inipUcnttim. The detailed description 

 of these three Richmond species follows. 



Batostoma vaiu.vns (James). 



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



Chwtetcs i-(irknis. James, Paleontologist, No. 1, 1S78, p. 2 (not figured). 

 MonticuUpora (Chdtctcs) rarinns. James, Paleontologist, No. 5, ISSl, p. 



36. 

 MonticuUpora variaiis. James and James, Jour. Cin. Soc. Nat. Hist., Vol. 



X, 1888, p. 177, 1)1. ii. Figs. 4a, -lb. 



' Goology of Minnesota, vol. iil, pt. i, p. 207, pi. 2G, figs. 38 40 ; pi. 21 

 figs. 0-in. 



2 Ibid., p. •-'!)!), pi. xxiv, fiR.';. 50. 



