THE NAUTILUS. 33 



12.6 in diameter. Two or three were toothless, the other had 

 3 teeth upon the lip. 



ASHMUNELLA TETRODON INERMIS n. SUbsp. PI. 1, fig. 7. 



Larger than the other forms, biconvex, indistinctly angular 

 above the middle in front, the periphery becoming rounded on 

 the last third of a whorl. There are 5J to 6 convex, closely- 

 coiled whorls, the last descending a little in front, guttered 

 behind the lip, swollen behind the gutter. Surface lightly 

 marked with growth-lines, without spiral strise. The aperture 

 has no teeth, or in some specimens shows extremely weak 

 traces of them. The lip is reflexed, the edge recurved, but it 

 is very narrow. 



Height 8, diam. 17.5 mm. 



Height 7.3, diam. 15 mm. 



Locality. — Station 69, Dry Creek. Also Station 63, where it 

 is rare. 



This is a smaller and especially more depressed shell than A. 

 mogollonensis, differing, moreover, by the noticeable peripheral 

 angle in front and the absence of spiral incised lines. While it 

 seems at first rather absurd to connect this form with A. tetrodon, 

 yet except by its greater size it does not differ in any important 

 respect from the least toothed of the variety mutator. We regard 

 it as a final stage in the degeneration of teeth, like Ashmunella 

 esuritor in the Chiricahuas. 



At first glance it seems to be without teeth, but it carries a 

 suggestion of teeth in the slight thickening of the lip in the 

 outer margin and a mere pimple at the basal position. Two in 

 twenty-four had two "pimples" at the basal position. Seven 

 had none. One with a " pimple " also had the mere suggestion 

 of a parietal lamella. Parietal callus thin and colorless. One 

 or two varix-streaks in every specimen, usually at or near the 

 end of the penultimate whorl. 



This colony and the next seem farthest removed from the 

 typical tetrodon. At this station also were found a few of the 

 full-toothed form of tetrodon, but without transitional specimens. 



Station 63. Growth-lines deeper than in Station 69. Shell 

 more depressed, larger. Three in six had the suggestion of a 

 basal tooth. 



