616 PALAEONTOLOGY OF ILLINOIS. 



rounded, mesial keel, bearing large, but not prominent, nodes 

 at intervals of about 0.8 mm. Entire obverse face between the 

 zocecia apertures very finely striated. Lateral branches short, 

 at their origin about three-fourths as wide as the midrib, ta- 

 pering rapidly toward their rounded distal extremities; opposite 

 or alternating, with eleven on each side in 1 cm., given off at 

 an angle of from 60 to 80. Zooecia in two alternating ranges. 

 Apertures sub-circular, with a very thin and slightly elevated 

 peristome, about 0.1 mm. in diameter, and 0.35 mm. apart; 

 eleven in 5 mm. They are arranged so that one is opposite a 

 lateral branch and one between. 



This species, though closely allied to several English and 

 Scottish species, is nevertheless quite distinct. Of American 

 forms P. vinei seems to be closer than any other, but differs in 

 being smaller and in having three zocecia where this has two. 



The specific name is given in honor of Mr. John Young, of 

 Scotland, who, chiefly in conjunction with Dr. Young, has done 

 so much to bring out the minute details of structure of their 

 Carboniferous Bryozoa. 



Position and locality: Keokuk group, King's Mountain, Ky., 

 and Keokuk, Iowa; also in the Cuyahoga shales of Ohio. 



PlNNATOPORA VINEI UMch. 

 PI. LXVI, fig. 5-5b. 



Zoarium pinnate; midrib slender, usually straight, 0.4 to 

 0.45 mm. wide, with the reverse side evenly rounded and finely 

 striated. Obverse face low ridge-shaped, the mesial carina 

 rounded, not prominent, with rather strong nodes at irregular 

 intervals. Lateral branches from one to two mm. in length, 

 like the midrib but only two-thirds as wide, oppositely or sub- 

 alternately given off from the sides of the midrib; nine or ten 

 in 1 cm. Zooecial apertures in two alternating ranges, fifteen in 

 5 mm., subcircular, with faintly elevated thin peristome, about 

 0.1 mm. in diameter. All the interspaces between the apertures 

 very finely striated longitudinally. 



The thinner midrib, longer lateral branches, and shorter zo- 

 cecia, distinguish this species from P. youngi with which it is 

 associated. 



