120 



BULLETIlSr Tl, UNITED STATES NATIONAL MUSEUM. 



ARTHROPORA SIMPLEX Ulrich. 



Text fig. 46. 



Arthropora simplex Ulrich, Fourteenth Ann. Rep. Geol. Nat. Hist. Surv. Min- 

 nesota, 1886, p. 65; Geol. Nat. Hist. Surv. Minnesota, vol. 3, pt. 1, 1893, p. 

 177, pi. 14, figs. 12-21. 



The identification of this neat little species in Russian strata is 

 based in part upon a small smgle specimen from Uxnorm, which 

 does not present all of the specific and generic characters because 

 the important pointed base for articulation with the preceding seg- 

 ment is broken away. That the species is undoubtedly present in 



Fig. 46.~Aethropoea simplex, a, several segments m theie natural position, life size; 6, surface 



OF A well-preserved FRAGMENT, Xl8; C, SEVERAL ZOCECIAL APERTURES OF THE SAME, X35; d, TANGEN- 

 TIAL SECTION, Xl8, SHOWING STRUCTURE OF THE DIFFERENT PARTS OF THE ZOARIUM; e, VERTICAL SECTION, 

 Xl8, ILLUSTRATING FORM OF ZOCECLA AND HEMISEPTA. BLACK RiVEE (DECOEAH) SHALE, MINNEAPOLIS, 



Minnesota. (After Uleich.) 



the Wassalem beds seems most certain from thin sections of speci- 

 mens accidentally encountered in the interior of limestone fragments 

 which were being studied for other species. To assist in the identi- 

 fication of the species a few of Ulrich's figures are introduced and 

 the following abridged description is inserted: 



Zoarium jointed, consisting of narrow, bifoliate, unbranched 

 stems, rounded and solid at the ends for articulation; averaging 18 

 mm. in length, 1.5 mm. in width, and less than 1 mm. in thickness. 

 Zooecial apertures elliptical and surrounded by a thin, granose peri- 



