58 



sulphate. Why the barytes should show a preferential selec- 

 tion of these empty annelid chambers, as is assumed in these 

 notes, is not very apparent, except on the general principle 

 that most minerals in solution show a tendency to undergo 

 precipitation on reaching a cavity in the rocks. 



DESCRIPTION OF PLATE IX. 



Fig. 1. Cast of vermiform-like object, entwined. Slightly 

 under natural size. 



Fig. 2. Cast of, apparently, two objects of a similar kind, 

 closely adjacent or intertwined with each other. Slightly under 

 natural size. 



Fig. 3. Cast of similar object, showing irregular twisting. 

 Natural size. 



Fig. 4. Cast in which the coils are more regularly arranged 

 in a spiral form. Natural size. 



Fig. 5. Another example, in which the coils are wound at 

 right angles to each other. The specimen is a fragment showing 

 fracture at both extremities. Natural size. 



Fig. 6. In this specimen the coils are wound around a central 

 axis in one plane, having a discoidal form. A head-like termin- 

 ation of the coil is seen at the upper margin. This example forms 

 an intermediate type between the worm-like casts on the one hand 

 and the discoidal "buns" on the other. Natural size. 



Figs. 1, 4, 5, and 6 agree in the diameter of their respective 

 coils ; and figs. 2 and 3 also agree with each other in this respect, 

 being somewhat smaller in diameter than the others mentioned. 

 In the two examples shown in figs. 2 and 3, slight constrictions 

 occur in the body whorls (especially where the latter make an 

 acute turn), which may have been caused by a succession of small 

 bulgings of an annulated soft body as the result of longitudinal 

 pressure. This feature, while quite distinct in the qbjects, is not 

 well shown by the photographs. 



