388 G. H. Girty — P seudorthoceras hioxense McChesney. 



would he elliptical. It is ornamented near the apex by very 

 tine, transverse and longitudinal stria? which hecome liner and 

 fainter above, so that all except the embryonic portion appears 

 almost absolutely smooth. One side of the shell (that on which 

 the apex lies) is marked toward the end by what may be a sort 

 of cicatrice. This structure is a minute ridge defined on each 

 side by a depression or sulcus, both ridge and sulci dying out 

 distally and losing themselves within a short distance in the 

 general curvature of the shell. Proximally tlie ridge is strongly 

 prominent, its end forming the apex of the specimen. It thus 

 resembles a minute rod projecting through the shell and end- 

 ing abruptly. Under strong magnification it seems to show a 

 very fine, longitudinal groove or slit. From what has been 

 said it will be apparent that these structures are developed on 

 the non-truncated side of the apex. The rest of the apical por- 

 tion shows little besides the sculpture, which is, however, more 

 or less modified in harmony with the configuration ; the annu- 

 lar markings are not parallel but converge toward the straight 

 side, thus apparently rounding over the end, and the longi- 

 tudinal lines also are somewhat curved. A stria distinctly 

 larger than the rest passes down the center of the straight side, 

 in line with the ridge of the cicatrice. 



The second specimen is less regular and less clear than the 

 other. The end has a crumpled look and is bent over so that 

 the apex projects beyond the plane of that side. A cicatrice 

 (a short raised line) is apparently present but it is oblique. 

 The concentric striae, rather more irregular and remote than in 

 the other specimen, can be distinctly seen, but the fine, longi- 

 tudinal markings are so extremely faint as to be doubtful. I 

 believe that they are really indicated. Their faintness, how- 

 ever, can hardly be ascribed to abrasion, for the other super- 

 ficial characters appear to be obscured little, if at all. 



DESCRIPTION OF PLATE I. 



Pseudorthoceras knoxense McChesney. 



Figs. 1 and 2. Two views of a specimen that has the end distorted. This 

 specimen does not show the longitudinal lines of the other, and the trans- 

 verse lines are farther apart. x 10. 



Figs. 3, 4, and 5. Three views of a symmetrical specimen. The very fine 

 cancellating sculpture is confined to the apical portion. Figure 3 shows the 

 straight side and figure 5 the curved side of the specimen as presented by 

 figure 4. x 10. 



Both specimens were obtained in the Des Moines group near Des Moines, 

 Iowa. 



