136^ SIXTEENTH KEPOKT ON THE CABINET OF NAT. HISTORY. 



ARTICULATA. 



GENUS SERPULITES ( M'Leay). 

 SERPULITES MURCHISONI. 



PLATE VI. FIG. 32. 



Serpulites murchisoni : Hall, Annual Report of Progress, Geological Survey of Wisconsin, 



1861, p. 48. 

 Geological Report of Wisconsin, 1862, Vol.i, p. 21. 



Body elongate, extremely compressed, very gradually tapering to 

 the acutely pointed apex, gently curved throughout its entire 

 length. Both sides (as they are imbedded in the sandstone) 

 very depressed-convex, with the margin of the aperture pro- 

 longed on the inner side of the curve. 



Surface of both sides marked by fine transverse lines of growth, 

 and by numerous strong somewhat equidistant undulations 

 parallel to the margin of the aperture. Length of a large in- 

 dividual two and a half inches, with a transverse diameter at 

 the aperture of three-tenths of an inch. 



The specimens of this species may have been circular when 

 living, as the prolongation of the margin of the aperture would 

 indicate ; this not always having the same relative position, and 

 the greatest extension being sometimes halfway between the in- 

 ner and outer angle. In these specimens the curvature is not quite 

 as great as in those where it is marginal, which would indicate a 

 tubular shell flattened in a direction oblique to the plane of the 

 curvature. 



This fossil occurs in some dolomitic beds of the sandstone at Lagrange 

 mountain in Minnesota, where it is associated with Dikelocephalus riiiiine- 

 sotensis and D. pepinensis. It has not been found, so far as at present 

 known, in any other locality. Its position, therefore, is in the later beds of 

 the formation. 



