770 THE PALEONTOLOGY OF MINNESOTA. 



[Nanno aulema. 



NANNO AULEMA, sp. nov. 



PLATE XLVII. FIGS. 411. 



The material which represents this interesting type of cephalopod structure 

 was collected by Messrs. E. 0. Ulrich, Charles Schuchert and the late W. H. Scotield, 

 from various localities in the Trenton series of Minnesota. No similar forms have 

 heretofore been found in the American faunas, and their novel character was 

 recognized and studied by the first two of these gentlemen. Like bodies had, 

 however, been found and described by Gerard Holm,'* derived from the lower Silu- 

 rian of Oeland and Esthland, and in the drift boulders about Eberswalde; they were 

 referred by him to the genus Endoceras, under the designation, E. lielemnitiforme 

 Holm, but we feel guilty of no temerity in regarding them as representatives of a 

 distinct type of structure. 



Our description is based essentially upon the American fossils, though supple- 

 mented by comparisons with the European species. 



The usual form which these bodies assume is somewhat that of a small Belem- 

 nites. The apical and posterior portion has a rounded, evenly tapering surface, 

 which would give it the form of a true cone were not one side, when the body is 

 viewed laterally, quite oblique, while the other is nearly vertical. Thus viewed the 

 shells are asymmetrical laterally, but as seen from the dorsal and ventral sides they 

 are bisymmetrical. After the conical expansion has extended for about one-half the 

 length of the body, there is a rather abrupt contraction on the oblique side and the 

 shell becomes more circular and much smaller in cross-section. Thus toward the 

 upper extremity of the shell a cylindrical tube is formed. 



The normal position, however, of the conical posterior portion is such that the 

 straight and the oblique side converge at the same angle; this diverts the cylindrical 

 or upper portion of the body to one side. 



These peculiar bodies are siphones; that represented in figure 10 shows the 

 oblique impressions left by the septa upon its surface, and figure 6 affords a concep- 

 tion of the relations of these siphones to the septate part of the shell. In the latter 

 is seen the central and symmetrical position of the apical cone with reference to the 

 entire shell, its abrupt contraction and the deflection of the cylindrical portion of 

 the sipho to one side. At the point where the contraction of the sipho begins, its 

 diameter is that of the shell, and from the apex to this point there is no trace of 

 septa. With the appearance of the septa begins the contraction of the sipho. That 

 the septa did not completely encircle the sipho beyond the diameter of the 

 siphonal funnels is shown by several of the specimens which present a smooth 

 surface on the dorsal or outer side, the marks of the septa being there 



1'i-liiT die Innere Organization elnlger stlurlscher Oephalopodea; Dames und Kayser's Palilontologlsche Abhand- 

 luneen. nd. III. Heft 1. pp. 40, pi. I, 1885. 



