-PLATE LXXXVXI— Continued. 
Myth, arc a fibristriata. 
Page 264. 
See Plate 33. 
Fig. 6. The left valve fig. 6, plate 33, redrawn to show the true form of the anterior side. This species is 
the only radiate form of the genus yet described and more perfect material may show 
characters which would exclude it from Mytilarca. 
Yellow sandstone. Burlington, Iowa. 
Mytilarca gibbosa. 
Page 262. 
See Plate 33. 
Fig. 7. The left valve fig. 20, plate 33, redrawn to show more clearly the entire form of the valve. 
Chemung group. Napoli, CattaraugusjCo., N. Y. 
Mytilarca (Plethomytilus) oyiformis. 
Page 255. 
See Plate 31. 
Fig. 8. The upper portion of a right valve showing the oblique posterior teeth of the hinge. 
Hamilton group. York, Livingston Co., N. Y. 
Modiola (Mytilops) metella. 
Page 268. 
See Plate 33. 
Fig. 9. A right valve showing the form and proportions of the shell. 
Chemung group. Warren, Pa. 
Mytilarca (Plethomytilus) arenacea. 
Page 253. 
See Plate 3.0. 
Fig. 10. A left valve. 
Schoharie grit. Schoharie, N. Y. 
Mytilarca occidentalis. 
Page 263. 
See Plate 33. 
Fig. 11. The left valve fig. 5, plate 33, redrawn to show the form of the beak and anterior side. The 
outlines of this one and of fig. 6 are partially restored from other specimens and represent all 
that can be determined from the imperfect material. 
Yellow sandstone. Burlington, Iowa. 
Gosselettia triquetra. 
Page 265. 
See Plate 31. 
Fig. 12. A large right valve of elongate form. 
Hamilton group. Piiltonham, Schoharie Co., N. Y. 
Mytilarca (Plethomytilus) Knappi. 
Page 256. 
Fig. 13. The right valve described, showing the form of the shell and the striated ligamental area. 
Hamilton group. Skaneateles lake, IV. Y. 
