194 



BULLETIN 77, UNITED STATES NATIONAL MUSEUM. 



Bryozoa has greatly extended the geographical range of this lower 

 form. The occurrence in the Black River-Trenton and in the Rich- 

 mond strata of a species or variety closely related to a Richmond 

 form, and with apparently no connecting links in the intervening 

 strata, is in line with other faunal similarities of these formations. 

 As shown by further study, this early occurrence of the common 

 Richmond species was described by Uhich as Atactoporella crassa, 

 but it is beheved to be more in keeping with the facts to regard it as 



Fig. 104.— Homoteypella hospitalis ceassa. Uleich's views of Atactopoeella ceassa. a, tan- 

 gential SECTION, X18, OF THE MINNESOTA TYPE; 6, VEETICAL SECTION OF THE SAME, X18, "WITH THE 



chakacteeistic tabulation of zocecia and mesopoees; c, seveeal zocecia in tangential section, 



X50, SHOWING THE STEUCTTJEE OF THE MOST MATUEE ZONE. CLITAMBONITES BEB OF THE LOWER 



Teenton, neae Cannon Falls, Minnesota. 



a variety of Prasopora, now Homotrypella, Jiospitalis. The reference 

 of Prasopora Iwspitalis to Homotrypella is also beheved to be nearer 

 the truth, because this species differs from typical Homotrypella only 

 in its massive form of growth. The following description is based 

 upon the Russian specimens. 



Zoarium massive, growth beginning upon some foreign object and 

 continuing until a more or less regular, rounded colony results. In 

 the Russian specimen figured, growth has been about a fragment of 

 a brachiopod, almost completely enveloping the shell. Surface 

 marked by moderately elevated, rounded monticules, 3 mm. apart. 

 Under a hand lens the surface is seen to be finely spinulose because 

 of numerous acanthopores. The characteristic features distin- 

 guishing this from most associated bryozoans are seen either in thin 

 sections or in fractures moistened and examined under a strong 

 hand lens. In either case the numerous cystiphragms lining the 

 zooecial walls and the closely tabulated mesopores are evident, while 

 the abundant acanthopores are seen to best advantage in tangential 

 sections. Cystiplu-agms are found most often lining one side of the 

 zocecia, but sometimes, as in figure 105 e, both sides show them. 

 Ordinarily 30 cystiphragms may be counted in 2 mm., while the 



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