PLATE XV. 



MONOMERELLA DuHHAMENSIS (page 57). 



Figure 1. Interior of the brachial valve, drawn partly from the actual test pre- 

 served on the smaller portion of the specimen represented on Plate 

 IX, fig. 1, and partly from a gutta percha mould of the cast of the 

 interior of that valve. 



Rhinobolus Galtensis, Billings. Sp. (page 59). 



Figure 2. Interior of the brachial valve, from a gutta percha mould of the cast of 

 the interior of that valve, from Gait, represented upside down by 

 figure 152, on page 168, of the first volume of the " Paljeozoic 

 Fossils." 



Ilionia Galtensis (page 68). 



Figure 3. An unusually perfect and well preserved left valve of this species, 

 drawn from a gutta percha impression of a natural mould of the 

 exterior of that valve, from Elora. 



Supposed Multispiral Opercula (page 97). 



Figure 4. Side view of one of these supposed opercula, from Flora, with the thin 



calcareous outer layer or sheath preserved, 

 " 5.- Similar view of a large specimen, from Elora, with the outer layer not 



preserved. 

 " 5a. View of the larger end of the same. 

 " 6. Longitudinal section of one of these opercula, three times the natural 



size, and slightly restored : a, the narrow, solid, multispiral, central 



axis ; &, a second slender, solid and tightly enveloping calcareous 



coil ; and c, the thin outer layer or sheath. 



IlljEnus Aboynensis (page 108). 



Figure 7. Imperfect cephalon of this species, from Aboyne, near Elora. 

 " 8. Pygidium of the same. / 



Pleueotomaeia Townsendii (page 77). 



Figure 9. Side view of the most perfect specimen known to the writer, drawn 

 from a wax impression of a natural mould of the exterior of a speci- 

 men from Durham, the slit band from the mould itself. 



