34 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 42. 



border of the cartilage of the snout. Above this pit there was an 

 overhanging ridge that ran forward from the pit about 15 mm. and 

 backward from it about 35 mm. In cleaning the specimen this ridge 

 split off and it was not replaced before photographing, in order that 

 the pit might be more distinctly shown. It seems not improbable 

 that the region below the hinder half of the ridge represents the orbit. 

 The process, 15, behmd the supposed nasal pit, may be the antorbital 

 process. 



In the dried skull of a shark at hand the interorbital region is 50 

 mm. wide. What may be the corresponding region of this Edestus, 

 possibly a still larger animal, has been compressed until it is only 10 

 or 15 mm. thick. Hence, the limits of the orbit may well be difficult 

 to distinguish. Moreover, as a result of the compression suffered, 

 the cartilage has been more or less fractured and faulted. The 

 upper border of the cartilaginous mass forms a smooth edge, except 

 just over the nasal pit, where some of it has been broken off. Where 

 the matrix has been removed from the left side of the upper shaft 

 the latter is seen to be covered by a layer of cartilage. This is sup- 

 posed to be the left side of the skull pressed against the shaft. It 

 is possible that a part of left palato-quadrate element is included. 



Behind the tooth indicated by 6, plate 1, the upper shaft is covered 

 with a mass of iron sulphide. This swelling probably does not rep- 

 resent any element of the skull. Beneath it, 7, is the base of a tooth, 

 the impression of whose apex is seen at 7, plate 2, figure 1. On the 

 broken hinder border of the block, at 16 and 17, are seen cross sections 

 of two other teeth, which seem to belong to the upper shaft. In case 

 the relations of the shaft to the cranium are such as they were in life, 

 the shaft must have extended far backward in the roof of the mouth. 



It is important to note that there is no indication of a pair of shafts 

 in either the upper or the lower jaw. This condition is in harmony 

 with the fact that all the tooth-bearing shafts that have been dis- 

 covered have been bilaterally symmetrical. Nor are there in this Iowa 

 specimen any signs of wear on the teeth, such as one would expect to 

 find. The specimen appears therefore to prove that the objects 

 which alone have hitherto represented the genus Edestus were pro- 

 duced in the mouth of the shark and that there was a sinde one above 

 and another below and that these played the one against the other 

 more or less closely. It is pleasant to credit Dr. C. R. Eastman with 

 having in various papers advocated the idea that the tooth shafts of 

 Edestus and related genera belonged in the mouth. He has been 

 disposed, however, to beheve that there was a pair of them in one jaw 

 or the other, probably the upper. The structure of these shafts 

 shows that each must have been produced by the consoHdation of a 

 median row of symphysial teeth. As, after the manner of sharks, 

 younger teeth were added to the hinder end of the series the older 



