SPECHTS FERRY BRYOZOAN FAUNA 



11 



differing somewhat from the characteristic structure of the species. These nine 

 specimens have more abundant mesopores and somewhat smaller zooecial apertures 

 than typical H. exilis. Zooecial apertures of these forms average 0.19 mm in maxi- 

 mum diameter exclusive of zooecial wall thickness, ranging from 0.14 to 0.24 mm 

 for 80 measurements on eight specimens. Further, these specimens typically (34 

 of 80 measurements on eight specimens) have nine zooecia and part of a tenth in 

 2 mm, measuring parallel to the length of the zoarium, and commonly (17 of 80 

 measurements on eight specimens) have either ten entire zooecia or ten complete 

 zooecia and part of an eleventh in this distance. Text figure 2 gives measurements 

 of the number of zooecia in a 2-mm distance and maximum apertural diameter of the 

 zooecia, exclusive of the zooecial walls, for these specimens. 



None of the Spechts Ferry specimens are assigned to H. minnesotensis , a 

 species described (Ulrich, 1895, p. 235) from the "Lower Third" of the Trenton 

 shales in the Minneapolis area. Although the diameter of some of the specimens 

 under study is slightly over 3.0 mm, many exceed 10 mm in diameter, and one 

 attains a diameter of 18 mm. The over-all size of the zoarium would suggest as- 

 signment of the specimens to H. minnesotensis and not to H. exilis , as Ulrich 

 (1895, p. 236) stated that the former species ranges from 5 to 15 mm in diameter 

 and the latter from 4 to 5 mm. However, as H. minnesotensis has distinctly thin 

 walls, the decidedly thick walls of the Spechts Ferry specimens militate strongly 

 against their placement in H. minnesotensis. Except for differences in zooecial 

 wall thickness and over-all size of the zoarium, H. minnesotensis and H. exilis 

 are strikingly similar in structure, particularly when examined microscopically. 



Distribution. — Localities 1, 2, 3, 4, 6, 8. 



Types. — Hypotypes, Illinois State Geological Survey, 12P2, 12P3, 12P5, 

 12P6, 12P8, 12P13, 12P14, 12P16, 12P17, 12P18, 12P20, 12P22, 12P23, 12P24, 12P26, 

 12P27, 12P29, 12P30, 12P33, 12P39, 12P40, 12P43, 12P45, 12P48, 12P51, 12P52, 

 12P54, 12P55, 12P56, 12P58, 12P59, 12P61, 12P65, 12P71, 12P72, 12P73, 12P95, 



35- 



30 



25 



qj 20 



Si 



O 



* IS. 



I 0- 

 5- 



7-7 + 9-9 + 



8-8+ IO-IOh 



ZOOECIA 

 IN 2 MM 



.24 .22 

 .23 .21 



.20 



18 



.16 



.19 .17 .15 



MAXIMUM APERTURAL DIAMETER 

 OF ZOOECIA, MM 



Text fig. 2 - Measurements on atypical forms of Homotrypa exilis 

 Ulrich. 7+ signifies seven entire zooecia and part 

 of eighth in a 2-mm distance. 



