190 Cincinnati Society of Natural History. 



Zoarium jointed; segments very slender, straight, needle- 

 shaped, 3 or 4 mm. long, quadrangular in cross section, 0.25 mm. 

 wide, 0.18 mm. thick, with zooecial openings on three sides, the 

 fourth being without them, but marked instead with four parallel 

 longitudinal striae. Zooecial apertures broad-oval, direct, o. n mm. 

 long, 0.09 mm. wide, enclosed by a sharply marked peristome. 

 Peristomes of each row of apertures joined together by a thin 

 ridge, having a length about equal to the larger or outer diameter 

 of the peristomes. Eight zooecial apertures in each row in 2.5 

 mm. A thin ridge, on each side of the range of apertures of the 

 obverse face of the segment, separates it from the lateral rows. 

 Apertures usually arranged alternately in the three rows. 



This species is closely related to A. tenuis, James, sp., but is 

 distinguished by having the non-celluliferous side narrower and 

 with fewer striae, causing transverse sections to be more nearly 

 square. The A. obliquus differs in having oblique zooecial 

 apertures. 



Position and locality: Base of Trenton Shales, near Minneapolis, 

 Minn. 



ARTHROSTYLUS OBLIQUUS, n. Sp. Fig 14, C, d. 



Zoarium jointed, segments very slender, needle-shaped, straight 

 or slightly curved, about 4 mm. long, subquadrangular in cross- 

 section, 0.2 mm. wide, 0.15 mm. thick, slightly expanding toward 

 the upper extremity. Zooecia in three rows occupying as many 

 faces of the segment, the fourth side with three longitudinal striae, 

 and no zooecia. Profile of a segment on an obverse or reverse 

 view, wavy on both sides; on a lateral view only on one side. 



Zooecial apertures small, oblique, the posterior margin very 

 prominent, arranged alternately m the three rows, with nine in 

 each, in 2.5 mm. A short ridge from the upper depressed edge 

 of each zooecial aperture is flanked on each side by the prolonged 

 lateral borders of the aperture. No ridge between the lateral and 

 central row of the zooecia. 



The oblique zooecial apertures, the prominent lower border and 

 absence of ridges between rows of apertures, distinguish this 

 species from A. conjunctus and A. tenuis, both of which it resem- 

 bles in other respects. 



Position and locality: Trenton Shales, Minneapolis, Minn. 

 Rare. 



