206 Nelson on Tertiary Mollusca of Peru. 



The depression for the animal is long and narrow ; muscular scar 

 deeply impressed. The length of this specimen is over 20 centim. ; 

 breadth 12*70 centim,; altitude of single valve 8'89 centim. 



Ostrea, sp. ind., b. 



Two valves were found, representing another species of this genus. 

 Shell is very narrow and long ; ligament scar broad and furrowed. 

 Length 144- millim, ; breadth 54*2 millim. 



Anomia, sp. ind. 



Single broken valves of a species of this genus occur in moderate 

 abundance, but without characters for determination. 



EXPLANATION OF PLATES. 

 Plate VI. 



Figure 1 . — Calliostoma noduliferum Nelson. 



Figure 2. — CaUopoma lineatum Nelson. 



Figure 3. — Aphera Peruana Nelson. 



Figure 4. — Polinices subangulata Nelson, young. 



Figure 5. — Marginella incrassata Nelson. The upper fold of the columella is not 



shown ; the edge of the outer lip in perfect specimens is evenly rounded. 

 Figure 6. — Marginella incrassata Nelson, dorsal view. 

 Figure 7. — Cancellaria Larkinii 'Nelson. 

 Figure 8. — Cancellaria Bradleyi Nelson. 

 Figure 9. — Dorsal view of the same. 

 Figure 10. — Cancellaria triangularis 'Selson. 

 Figure 11. — Solarium sexlineare Nelson. 

 Figure 12. — Polinices subangulata Nelson. 

 Figure 13. — Ventral view of the same. 



Plate VII. 



Figure 1. — Argobuccinum Zorritensis Nelson. 



Figure 2 — Ventral view of the same. 



Figure 3. — Cuma alternata Nelson. 



Figure 4. — Dorsal view of the same. 



Figure 5. — Area Larkinii Nelson. The umbos are denuded, showing thin, acute rib?. 



Figure 6. — Lateral view of the same, in perfect preservation. 



Figure 7. — Interior of the same. The ligament area is denuded, showing radiating 



striae. 

 Figure 8. — Leda acuminata Nelson. 

 Figure 9. — Crassatella gihbosa Sowerby. 



All the figures are natural size, from photographs made by Mr. Sidney I. Smith. 



