150 A New Genus of Cambrian Pteropods 



species is in the condition of a flexible whip or tail, and as pre- 

 served in the shale it is not nnfrequently twisted from the plane 

 in which the principal part of the shell is flattened, and it is also 

 frequently bent away from the axial line of the cone to the right 

 or left. In some cases, the larval region of D. hyattiana is 

 preserved in the shale as a flattened cylinder ; in others, as a very 

 slender, slowly-expanding tubule ; but in all cases it is crossed by 

 distinct annulations about as far apart as the tube is wide, and of 

 a firmer texture than the interspaces. Whether the projection of 

 these nodes is due to a thickening of the tube, or to transverse 

 diaphragms within, does not clearly appear, but the latter alterna- 

 tive seems the more probable one. 



The mucronate point in which the apex of most species of 

 Hyolithes terminates, may be seen to have been formed in the 

 upper part of the larval region in some specimens of D. hyattiana ; 

 but others have not got it. This variation of the presence or 

 absence of the mucronate point at the top of the larval tubule, 

 shows how and where the thickening or calcification of the 

 shell began, and renders it probable that all of the Hyalithoid 

 shells began in a similar larval tube, but that in most of them 

 the tube became deciduous, or was absorbed. 



The possession of a septate region is perhaps the feature by 

 which this genus of pteropods can most readily be recognised, or 

 at least separated fron the ordinary Hyolithes. This region is 

 well shown in two species of this genus, C. gracilis (n. sp.), and 

 C. daniana (Hyolithes danianus, Bulletin No. 10, U. S. Geolo- 

 gical Survey). It is marked by a more or less rapid expansion 

 of the cone, by added firmness of texture in the shell, and by the 

 presence of several transverse septa, crossing the cavity of the 

 shell. The chambers thus produced are not known to be con- 

 nected by a siphon. This part of the shell, as preserved in the 

 shale, is always more terete than the rest; owing either to its 

 firmer outer shell, or to the support given by the septa, or to a 

 more perfectly rounded contour during the life of the occupant. 

 In the species of this genus, the conical shell expands less 

 rapidly above the septate space than in it. C. gracilis (n. sp.) 

 may be taken as the type. 



The modern genus Cuvieria possesses a septate shell which has 

 some features in common with Camerotheca, but the lower part 



