EAELY PALEOZOIC BEYOZOA OF THE BALTIC PROVIXCES. 245 



ERIDOTRYPA -EDILIS MINOR (Ulrich), 



Text fig. 139. 



Eridotrypa mutahilis var. minor Ulrich, Geol. and Nat. Hist. Surv. Minnesota, 

 vol. 3, pt. 1, 1893, p. 266, pi. 26, figs. 20, 21, 29, 30. 



This varietal name was proposed for specimens differing from the 

 more common form mainly in their internal structure. These differ- 

 ences, quoting from Ulrich, are as follows: 



First, the central tubes are unusually large and their walls more wavy than in 

 typical mutahilis; second, the tubes altogether seem to have been developed more 

 regularly, and their width in the peripheral region somewhat less; and third, dia- 

 phragms are wanting throughout the greater part of the axial region. Under ordinary 



Fig. 139.— Eeidoteypa ^dilis minok. Copied from Ulrich's figures of Eridotrypa mutabilis 

 minor, a, 6, and c, three average fragments; d, surface of a fragment, x9; 6, tangential 



SECTION, X18; /, VERTICAL SECTION, X18. LOWER PART OF TrENTON LIMESTONE, NEAR CANNON FALLS, 



Minnesota. 



circumstances these differences would be considered as of specific value, but in this 

 instance, knowing the extreme variability of the species, I can not credit them with 

 more than subordinate importance. 



Occurrence. — ^Variety minor is known only from the lowest Trenton 

 at Cannon Falls, Minnesota, and from the Wesenberg limestone (E) 

 at Wesenberg (Cat. No. 57318, U.S.N.M.). 



British Museum, represented by specimens from American locali- 

 ties. 



ERIDOTRYPA EXIGUA Ulrich. 



Text fig. 140. 



Eridotrypa exigua Ulrich, Geol. and Nat. Hist. Siu"v. Minnesota, vol. 3, pt. 1, 

 1893, p. 266, pi. 26, figs. 17, 18. 



Original description. — Zoarium small, branches very slender, several hundred frag- 

 ments varying in diameter from 0.6 to 1.0 mm. ; bifurcations apparently remote. Some 

 of the fragments are pointed at the lower end, indicating a free condition of the zoa- 

 rium, or an articulation like that of Escharopora. The eastern form of the species is 

 usually a little stronger than the average of the Minnesota types, the specimens 

 seen from Vermont and New York being mostly 1.0 mm. or a little more in diameter. 



