Pinna lata.
Fig. 4. View of type, a left valve.
Pleurophorus whitei.
Fig. 5. Type specimen; cast of a left valve on the same slab as the two following and the cephalothorax of a large limuloid. Fig. 5a. Cast off a broken specimen, showing the anterior muscular impressions. Fig. 5b. Specimen of different outline.
Allorisma kansasensis.
Fig. 6. Imperfect cast, showing strong concentric undulations impressed upon it. Fig. 6a. Lateral view of type. Shell exfoliated in front.
PLATE V.
VARIATION OF THE SPIRALIA IN SEMINULA ARGENTIA
(Shepard) Hall.
BY J. W. BEEDE.