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PROCEEDINGS OF THE NATIONAL MUSEUM. 



VOL. 39. 



stolon, is of uniform diameter for some distance in the elon- 

 gated forms. The gradual increase in diameter begins with the 

 zooecium proper. The dimensions for the various forms of the 

 species are as follows: The zooecia in the slender, elongate form 

 shown in figure 6 average seven in 8 mm., while each, including 

 the stolon, is from 1 mm. to 1.5 mm. long and from 0.11 mm. to 

 0.18 mm. at its greatest diameter. The slender proximal or sto- 

 lonal portion in this form, as well as the others to be mentioned, is 

 about 0.04 mm., while the aperture itself is slightly wider, averag- 

 ing 0.05 mm. In figure 7 the short form of the species is illus- 

 trated. Here the measurements are practically the same as those 

 given above, except that the zooecia vary from 0.6 mm. to 0.8 mm. 



Fig. 7.— Coetnotrypa delicatttla. Specimens figubed by Uleich as Stomatopora pbotttana. 

 a, fragment of a zoarittm, x9; b and c, two groups of zocecia, x25; d, several zocecia op 

 UNUSUAL SIZE, X25. Ordotician, Black River group, St. Paul and Minneapolis, Minnesota. 

 (After Uleich.) 



in length, and 8 to 10 occur in 5 mm. Several unusually large 

 zooecia are illustrated in figure 7d, but such specimens are of rare 

 occurrence and even here the measurements are all in proportion 

 to those of the typical specimens. In all of these various speci- 

 mens the length of the zooecium proper is approximately the same 

 and its angle of divergence remains about 15°. 



The considerable variation in the length of the stolon of this 

 species has been discussed before and specific differences based upon 

 this character have not been maintained, as noted in the synonymy 

 above. At certain horizons, particularly in the McMillan formation 

 at Cincinnati, Ohio, very luxuriant growths of C. delicatula are found 

 and it is in such specimens that the greatest variation is exhibited. 



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