964 THE PALEONTOLOGY OF MINNESOTA. 



LLophospira biolncta. 



Surface, the basal half chiefly, usually with large though not very prominent 

 revolving ribs. Lines of growth recurving moderately toward the peripheral band, 

 indicating a wide but not very deep sinus in the outer lip. Species: Pleurotomaria 

 ohioensis James, PI. robusta and var. Icevissima Lindstrom, PI. trilix Hall. 



D. Trochonemoid.es section: In all respects like Trochonema save that the 

 supra-peripheral keel bears a distinct band. Differs from ordinary types of 

 Lophospira in the relatively depressed form, large umbilicus, thick shell and oblique 

 mouth. Species: L. trochonemoides Ulr., L. knoxvillensis Ulr., L. notabihs Ulr. 



LOPHOSPIRA BICINCTA Hall, 



PLATK LXXII, FIGS. 1-5. 



Murchisonia bicincta HALL, 1847, Pal. N. Y., vol. i, p. 177, pi. xxxvm, flgs. 5a-5/, (?5g and 5h.) 

 Murchisonia milleri HALL', 1877, 1st Ed. Miller's Amer. Pal. Fossils, p. 244. 



Might 15 to 30 mm.; apical angle 59 to 63, usually about 60. Volutions five 

 or six, subangular; last one ventricose below, tricarinate, the upper ones bicarinate 

 the lower carina being hidden by the suture; central or peripheral angle margined 

 on either side by a sharp elevated line, with a narrow groove between, the angle, 

 therefore, being composed of three lines of which the central one is a little stronger 

 and more prominent than the lateral ones; lower carina thin, abruptly raised, the 

 space between it and the peripheral angle scarcely concave and almost perpendicular; 

 upper carina sharp, rather strong, removed a little more than a third of the 

 biconcave upper slope of the volution from the suture; aperture somewhat obliquely 

 subelliptical, higher than wide, narrow below, subangular at the lower inner corner; 

 inner lip but little thickened, slightly twisted, never completely covering the minute 

 umbilicus; outer lip very slightly sinuate. Surface marked by fine sharp subequal 

 striae, curving backward very gently from the suture to the peripheral band; 

 beneath the latter they pass in a vertical direction to the lower carina which 

 scarcely interrupts their course to the umbilicus, near which only a slight backward 

 curve is noticeable. On the most perfect specimen seen all the transverse lines 

 present the appearance of being minutely papillose or toothed, while the central 

 line of the peripheral band is crossed by straight lines of which there are nearly 

 twice as many in a given space as of those coming from above and below. 



The most marked and important feature of this species is the exceeding 

 shallowness of the sinus or notch in the outer lip. It is true Prof. Hall mentions 

 an abrupt retral and forward curve of the surface striae at the mesial band, but if 

 we accept his fig, 5e as correct, it is evident that this statement is quite at variance 

 with his illustrations. We prefer to accept the evidence of the cited figure upon 

 the point in question rather than the description, especially since it is not at all 



