BRYOZOA. 641 



Tliis variety differs from the typical form of the species in 

 having smaller, and more regularly arranged fenestrules. The 

 zooecia apertures also seem to have been somewhat smaller, but 

 this point was not determined satisfactorily. 



Position and locality: Lower Coal Measures, Seville, 111. 



ARTHROCLEMA Billings, 1862. 



(Palaeozoic Fossils, vol. I. p. 54.) 

 (For generic diagnosis see page 400.) 



ARTHROCLEMA ANGULARE Ulrich. 



PI. XXIX. fig. 6. 6b. 



Of this species I have seen only isolated segments, but there 

 can be no question as to their generic relation. The primary 

 ments are four mm. in length, about one mm. in diameter, 

 somewhat irregularly cylindrical, with the ends slightly thick- 

 ened, solid, the proximal extremity obtusely pointed, the upper 

 only convex and faintly indented at the center. On two oppo- 

 site sides of the segments there is a large and rather shallow 

 socket, situated a little below the middle of the length. The 

 secondary segments are six-sided, 5.5 mm. in length, 0.5 mm. 

 or very little more in diameter. Zooecia with narrow oval aper- 

 tures, 0.07 mm. wide, 0.17 mm. long, seven in three mm. ar- 

 ranged in longitudinal series, between the strong bounding 

 angles of the slightly concave sides of the segments. The lower 

 margin of the apertures is more prominent than in front, and 

 generally drawn out posteriorly. On the primary segment the 

 zooecia are less regularly arranged, and the interspaces between 

 the apertures flexuously striate. especially in the vicinity of the 

 articulating sockets. Tertiary segments not observed. 



In most respects the above species agrees with A. pulchelluni 

 Billings, from the Trenton of Canada. Before me I have a 

 number of very fine specimens of that species, showing that 

 both the primary and secondary segments are longer in the 

 Illinois species, those of the Canadian examples being quite con- 

 stantly two or three ram. in length. The cells are also a little 

 smaller and closer together, there being six in two mm.; the 

 80 



