TWENTY-FOUBTH ANNUAL MEETING. 



39 



in most forms of this genus. They are covered by numerous well-defined straight 

 pilse, terminating in small nodes at the edges of the abdomen. The abdomen is 

 convex, with a narrow, slightly-depressed zone along the center. The shell is orna- 

 mented by prominent strias of growth, and at regular intervals one of these is more 

 prominent than the neighboring striations, showing frequent short arrests of 

 growth. These striae are straight upon the sides, but upon the abdomen bend sud- 

 denly posteriorly, forming wide sinuses of great depth; doubtless the aperture was 

 similar. The sutures are almost straight on the sides and have a very broad and 

 slight ventral lobe. Siphuncle unknown. 



This shell is very similar to Nautilus falcatus L. de C. Sowerby, [see Prestwich, 

 Geol. Ccalbrookdale, Trans. Geol. Soc. London, V, pi. 40,] in so far as they both 

 have ribs. The Coalbrookdale specimen, however, has no tubercles, or at least none 

 are given, and the sides of the whorl are figured as concave. Naut. Nikitini Tzwe- 

 taev, [see op. cit., pi. I, fig. 5,] is also very similar, but the ribs are less numerous 

 and the sutures quite different. Nikitini has saddles and lobes as in Tainoceras. 

 Living chambers were not observed. Position of siphuncle is unknown. 



Figs. 3 and 4 show the fragment, and fig. 5 is therefore in part a restoration. 



' ^!^.■-■;:;t|•>;^•vVV:■•^■'• 



^. \ 







■'V'/:.'.-.:. •■.:■•, •.■■ ■■■■ v.*i-.;- -■•■■;:•.■. -Krij''" 



Fig. 6. 



METACOCEEiS DUBIUM, n. S. 



