Legend: 
Fig. 1. 
Fig. 2. 
Fig. 3. 
Fig. 4. 
Fig. 5. 
Fig. 6. 
Fig. 17. 
PLATE 30. 
D. Deltarium. A. Delthyrium. 
T. Syrinx. j. Cardinal process. 
s’. Rostral callous. a. Adductor scars. 
d. Dental lamelle. r. Diductor scars. 
SYRINGOTHYRIS, A. WivcHeEt1. 
Page 760. 
Syrmncotuyris typa, A. Winchell. 
The interior of the apical portion of a pedicle-valve; showing the dental 
plates and syrinx. 
The interior of another pedicle-valve; showing the greatly thickened 
syrinx inclosed along its posterior surface. 
Burlington limestone. Burlington, Iowa. 
SYRINGOTHYRIS suBcUSPIDATA, Hall. 
The interior of a large pedicle-valve; showing the rostral callous, the 
extension of the syrinx and the muscular scars. 
Keokuk group. Nauvoo, Illinois. 
SyRincotuyRis Texta, Hall. 
The central cardinal portion of the pedicle-valve; showing the trans- 
verse rostral plate, and the free, completed extremity of the syrinx, 
which is elsewhere adherent to the inner surface of the plate. 2. 
The central cardinal portion of an internal cast of conjoined valves ; 
showing impressions of the cardinal process, dental plates and the 
filling of the tubular portion of the syrinx. 
Ventral view of an internal cast; showing the muscular scars of the 
pedicle-valve. 
A transverse section, showing the form and extent of the spiral cones. 
. A transverse section of the pedicle-valve a short distance below the 
apex; showing the dental plates resting on the bottom of the valve, 
the transverse plate and the adherent syrinx. 
212 
