PLATE XXVIII—Continued. 
(^YRTINA TRIQUETRA, Hall. 
Figs. 34, 35. Views of an average specimen; showing curvature of the umbo and height of the cardinal 
area. X 2. 
Hamilton group. Roclc Island, Illinois. 
CyRTINA LACIIRYMOSA, Sp. IIOV. 
Figs. 36, 37. Views of an average example ; showing the i-egular, slightly incurved cardinal area, and the 
sparsely pustulose exterior. X 2. 
Fig. 47. An enlargement of the exterior; showing the large pustules of various sizes. X 5. 
Waverly group. Richfield, Ohio. 
CVRTINA ACUTIROSTRIS, SllllinaiTl. 
Fig. 38. An exterior of a brachial valve, unusually extended on the hinge. X 2. 
Figs. 39-42. Views of a normal example ; showing the high, incurved cardinal area in figures 39 and 40, 
and the strongly lamellose or squamous exterior of the valves in figures 41 and 42. X 2. 
Fig. 44. A portion of a transverse section of the umbonal region of a specimen in which the deltidial cov¬ 
ing is lacking; showing the cavity or tube formed at the union of the dental lamellae with the 
median septum. X 3. 
Fig. 54. The deltidial portion of the pedicle-valve, in which but a part of the deltidial covering is retained ; 
showing the edge of the median septum peneti-ating the deltidial cavity. X 3. 
Choteau limestone. Pike coimity, Missouri. 
