EARLY PALEOZOIC BEYOZOA OF THE BALTIC PEOVINCES. 



151 



ARTHROCLEMA ARMATUM Ulrich. 



Text fig. 73. 



Arthroclema armatum Ulrich, Journ. Cincinnati Soc. Nat. Hist., vol. 12, 1890, 

 p. 194, figs. 19 a-d (not e-h= Arthroclema pulchellum Billings); Geol. Nat. 

 Hist. Surv. Minnesota, vol. 3, pt. 1, 1893, p. 201, pi. 2, figs. 8-11, 25, 28-33; 

 pi. 3, fig. 7. — Simpson, Fourteenth Ann. Rep. State Geologist New York for 

 the year 1894, 1897, p. 547, fig. 111.— Sardeson, Journ. Geol., vol. 9, 1901, 

 p. 161. 



This species is represented in the Russian collections by a few speci- 

 mens showing no lateral articulations. Had not the American form 

 been so well figured and represented in the collections of the United 

 States National Museum it would have been almost impossible to 



Fig. 73.— Aethkoclema armatum. a, large segment of the primary series, showing a sharply 

 defined, articulating socket, natural size, and xl8; 6, opposite side of another segment of 

 the primary set, x18; c, a segment of the tertlary series, x18; d, complete segment of the 

 secondary set, x 18. lower part of the trenton limestone, cannon falls, minnesota. (after 

 Ulrich.) 



have made such a close determination. However, the Russian speci- 

 mens agree exactly with the tertiary segments of Arthroclema arma- 

 tum, and I have no doubt that in time additional material will prove 

 the correctness of the determination. 



These tertiary segments are 2.5 to 3.5 mm. long and 0.3 mm. or 

 less in diameter, five or six sided, with the angles fairly prominent, as 

 shown in figure 73 c, which represents the tertiary segment of an 

 American example, quite similar to the corresponding Russian 

 specimens. 



The greater strength of the secondary segments, but their evidently 

 close relation to the tertiary ones, is indicated in figure 73 d, while 

 the short, compressed, irregularly shaped primary segment, with the 



