MR, T. W. BRIDGE ON THE OSTEOLOGY OF POLYODON FOLIUM. 
731 
The remarkable correspondence in so many features between the Elasmobranchs and 
the Selaclioid Ganoids is readily explicable on the view of their community of descent, 
and the retention of many ancestral structures in both groups ; and any support which 
this agreement may lend to the view of the direct descent of the Ganoids from the 
Elasmobranchs is very much diminished in value by the existence of other facts, 
previously referred to, which strongly points to the monophyletic origin of the 
Amphibian and Ganoid stocks. 
Description of the Plates. 
The figures are nearly all of life-size, and the lettering is uniform throughout. The 
cartilage is tinted blue, the cartilage bones are coloured yellow, while the membrane 
bones remain white. 
u 1 . Dermo-ethmoid. 
cr, a 3 , and a 4 '. Rostral splints belonging to the medio-dorsal series. 
b l . Parietals. 
b~. Frontals. 
b 3 , b 4 , and b b . Rostral splints belonging to the supero-lateral series. 
b.br 1 . First basibranchial element. 
b. tp. Basitemporal ala. 
c 1 . Post-temporal. 
cr. Dermo-sphenotic. 
c 3 . Nasals or dermo-prefrontals. 
c. br 1 ., c.br 4 . Cerato-branchials. 
c.h. Ceratohyal. 
D. Dentary. 
ep.br. Epibranchial. 
h.m. Hyomandibular. 
h.hy. Hypohyal. 
h. br. Hypobranclnal. 
i. hy. Interhyal. 
i.op. Interop ere ulum. 
mg.o. Dorsal or ventral marginal ossicles of rostrum. 
m.pg. Mesopterygoicl . 
mt.pg. Metapterygoid ligament. 
mx. Maxilla, 
MJc.c. Meckel’s cartilage. 
op. Opisthotic. 
