76 THE PALEONTOLOGY OF MINNESOTA. 



IRuffella. 



other spicules in such a manner that a network with rhomboidal meshes is formed. 

 Similar but smaller spicules are developed in the interspaces. This regular arrange- 

 ment of the spicules is but rarely met with, the surface appearing, as already stated, 

 usually to be striated in a longitudinal direction mainly. On an average eleven 

 of the stria? occur in 5 mm. transversely. 



" Inner layer of sponge .tissue exceedingly thin and minutely porous. Its struct- 

 ure has not been determined, the finer details having been obliterated during the 

 process of fossilization. 



" This sponge cannot be confounded with any other fossil ftnown to me from 

 Cambrian or Silurian rocks, its finger-like form and the strong thread-like striations 

 of the surface giving it a very characteristic and easily recognized aspect." 



Formation and locality. Common in the Trenton shales at Minneapolis, St. Paul, Oxford Mills, 

 Fountain, Preston, and near Marion, Minnesota ; Decorah, Iowa. ?In the Galena shales, six miles south of 

 Cannon Falls, Minnesota. 



Collectors. -Miss Cora E. Goode, E. O. Ulrich, C. L. Herrick, J. C. Kassube, W. H. Scofleld, and the 

 writers. 



Mas. Beg. Nos. 712, 713, 3491, 4946, 5020, 7702-4, 7707, 7708. 



RAUFFELLA PALMIPES Ulrich. 



PLATE F. FGS. 19, 20. 



1889. Bauffella palmipes ULBICH. American Geologist, vol. iii, p. 238, fig. 3 on p. 236. 



Original description. " Sponges rather large, originally probably of inverted pear- 

 shaped outline, consisting of five bi- or tri-furcating compressed lobes springing from 

 a short stem, united at the center and arranged in a radial manner. In the fossil 

 state they present varied forms corresponding with the degree and direction of the 

 compression they have suffered. This is much less than might be expected of so 

 frail an organism, and I can account for the comparatively good preservation of the 

 shape only by supposing the lower extremity of the stem to have been open, thus 

 permitting the material that made up the strata (mud, fragments of shells, bryozoa. 

 etc.) to enter freely into the internal cavity. Generally, the cavity is entirely filled 

 with material of the same nature as the surrounding matrix. In a few cases 

 free communication must have been interrupted causing a lobe to remain empty 

 and now to appear much more compressed than usual. On account of the friable 

 nature of the shales in which they are found, most of the specimens are mere frag- 

 ments. Still, after a careful search, the author succeeded in securing three nearly 

 complete examples. Two of these are compressed obliquely with the stem on one 

 side, and look very much like the webbed foot of a bird. The specific name was 



