32 THE NAUTILUS. 



striate. The most fully toothed example (pi. 1, figs. 3, 3a) 

 agree with A. tetrodon, except that the parietal tooth is smaller. 

 There are other examples, with all of the teeth smaller than in 

 tetrodon, and still others, found with them (No. 60 A) have the 

 lip-teeth very small, partly wanting, the parietal tooth either 

 wanting or minute (pi. 1, figs. 4). This is the only instance 

 where almost fully toothed tetrodon and mutator occur in the same 

 colony ; but without transitional individuals. 



Lots from Stations 67 (pi. 1, figs. 6, four adult shells) and 

 78 vary from shells having four small teeth (like the tetrodon 

 from Station 60) to shells having only weak rudiments of teeth. 

 The lots from these stations therefore connect tetrodon and mu- 

 tator, and cause us to rank the latter as a variety of the former. 

 The varying condition of the teeth in different colonies may be 

 briefly indicated in a few, to give an idea of this variation. 



Station 78. In nineteen examples, 10 were toothless ; 2 had 

 a full set of teeth and a lamella ; 3 had a lamella and thickened 

 in both lip positions ; 1 had a lamella only ; 4 had three "pim- 

 ples " upon the lip in place of teeth, no lamella ; 1 had a "pim- 

 ple" at the basal position. Diameter 12 to 14.5 mm. 



Station 61. Eight had a full set of teeth and lamella ; 13 had 

 teeth upon the lip in different degrees of development. 1 had 

 a lamella only, 6 were toothless. Diameter 13.4 to 15.2 mm. 



Station 62. In 75 shells 12 had a lamella and a full set of 

 teeth, varying from mere ' ' pimples ' ' to fully developed teeth, 

 28 had a full set of teeth on the lip only, also varying as much 

 in development, 19 with one or two basal teeth, only 12 without 

 teeth. Nearly all were dead or broken shells. Diameter 14.6 

 to 11.4 mm. 



Station 67. Coarser growth-lines and striations more distinct ; 

 not guttered deeply back of the lip ; angulation more pronounced, 

 umbilicus enlarged in the last half of last whorl. Spire more ele- 

 vated than the two preceding colonies. Diameter 12^ to 14 mm. 



In a lot of 125 (dead and broken) 34 had a lamella and the 

 full set of teeth, 54 had three teeth upon the lip, 6 had a basal 

 tooth only, and 11 were toothless. 



Station 68. Same as the preceding, but smaller and smoother. 

 Nine were collected alive. These measured 7 mm. in alt. and 



