Cretaceous Selachians 
85 
imum width (although the right lateral cusp and a small portion of the 
root are missing). It bears a sigmoidal lateral cusplet alongside a slender, 
slightly sigmoidal central cusp. 
Discussion : — The teeth of P. arcuata are quite common in beds of Late 
Campanian to Middle Maesjxichtian age but quite uncommon in the 
Late Maestrichtian. This specimen is not definitely identifiable as P. 
arcuata , and its temporal occurrence is very late for that species. 
Order BATOIDEA 
Suborder GANOPRISTINIDEA 
Family SCLERORHYNCHIDAE 
Ischyrhiza Leidy, 1856 
Ischyrhiza mira Leidy 
Ischyrhiza mira Leidy, 1856:221. 
Material : — PU 22427A-B, two rostral teeth (Figs. 27-30); three other 
rostral teeth (no oral teeth). Site 1. 
Description : — Rostral teeth of rather large size, ranging in length from 
3.5 to 5.5 cm. No barb present on the lateral edge of the enameloid cusp 
(as in Onchopristis) and no plications or striations on the enameloid faces. 
The root base bears strongly rugose pleats which probably strengthened 
the attachment to the rostral cartilage. Otherwise the rostral teeth are- 
characteristically sclerorhynchoid. 
Discussion : — Rostral teeth of the sawfish Ischyrhiza are common in Up- 
per Cretaceous deposits of North America, especially in the range from 
Late Campanian to Middle Maestrichtian. This genus is unknown out- 
side the continental limits of the United States, for, as noted in previous 
work (Case 1967), Sclerorhynchus replaces Ischyrhiza in the Upper 
Cretaceous deposits of Europe and North Africa. Originally the rostral 
teeth of Ischyrhiza were thought to be the oral teeth of a teleost fish (Leidy 
1856; Fowler 1911) but were later identified as belonging to a primitive 
sawfish that is known as a ganopristine because its denticles have a com- 
bination of enameloid and osseous structure. 
Suborder DASYATOIDEI 
Family MYLIOBATIDAE 
Rhombodus Dames, 1881 
Rhombodus cf. R. binkhorsti Dames 
Rhombodus binkhorsti Dames, 1881:1, Fig. 1. 
Material : — PU 22428, a pavement tooth (Figs. 31-35); and a dozen ad- 
ditional specimens. Sites 1, 2 and 3. 
