SCALES AND DERMAL TEETH OF SOxME GANOID AND PLACOID FISH. 475 
Fig-. 31. Horizontal section of the shagreen of the common Dog-fish, the bases and 
apices of the dermal teeth being alike ground away. The faint ring 
surrounding each areola is produced by the form of the tooth ; the upper 
section having divided it at a narrower point than the lower one, thus 
shows a portion of the surface of each. 
Fig. 32. Vertical section of one of the dermal teeth of fig. 31. 
Fig. 33. Vertical section of the fossil shagreen of the Hybodus reticulatus. 
Fig. 34. Vertical section of the surface of the snout of the common Saw-fish {Prdstls). 
Magnified 65 diameters. 
Fig. 35. Vertical section of the premaxillary bones of a Coelorhynchus. Natural size. 
Fig. 36. Profile view of part of the same organism. Magnified 6 diameters. 
Fig. 37 . Horizontal section of portions of two segments of the same. Magnified 
9 diameters. 
