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6 FIELD COLUMBIAN MUSEUM ZOOLOGY, VOL. i. 



the two elements named, and that in the caudal region of this fish 

 we have both of these elements present, and still distinct from each 

 other. I find it impossible to ignore the results of palaeontological 

 researches when they are exhibited in so clear a light. These results, 

 which reveal an extraordinary similarity between the stegocephalous- 

 vertebral column and that of so many of the earlier osseous fishes, 

 cannot be set aside lightly, merely because there is in the tail of cer- 

 tain Elasmobranchs an evident duplication ; at -least not until it has 

 been shown by embryology that the vertebral bodies in the two cases 

 arise in the same way ; and this has certainly not yet been done. 



If we shall regard a pleurocentrum and a hypocentrum in the tail 

 as together constituting a vertebral body, the total number of these 

 in the whole vertebral column will, of course, be considerably reduced 

 below the number usually given by authors. Franque says that the 

 number, including the intercalated ones, is commonly ninety-two, 

 although the number may vary somewhat. Of this number thirty- 

 seven or thirty -eight belong to the trunk. L. Schmidt found in one 

 skeleton thirty-nine vertebrae in the trunk and forty-seven in the 

 tail. In his figure of another specimen he represents fifty segments in 

 the tail, of which about fourteen are the so-called intercalated pieces. 

 The anterior four to six caudal vertebrae are simple, and resemble in 

 all respects those of the hinder dorsal region, except that the lower 

 arches are closed below to form the haemal canal. Near the end of 

 the tail, again, the intercalated pieces are not developed. Therefore, 

 counting pleurocentrum and hypocentrum as one, we find about sev- 

 enty-five vertebra? in the whole column, although the number may be 

 from one to three less. 



Externally the vertebrae of Amia differ from those of most other 

 osseous fishes in the almost total lack of excavations, bony ridges and 

 subsidiary processes. Those of the trunk especially may be regarded 

 as approximately circular disks, each with a conical excavation at each 

 end. These disks become gradually shorter as we move from the 

 hinder dorsal vertebrae towards the head. In the tail the two ele- 

 ments, pleurocentrum and hypocentrum, taken separately, are con- 

 siderably shorter than a hinder dorsal vertebra ; but, if we consider 

 the two elements as constituting a single vertebral body, we find that 

 their combined lengths usually exceed somewhat that of a dorsal cen- 

 trum, while the length of an anterior caudal vertebra is only about 

 seventy-seven per cent of that of a hinder dorsal vertebra. As far for- 

 ward as the twenty-third dorsal vertebra from the head the length of 

 each vertebral body remains nearly the same as that of the hinder- 

 most. In front of this they generally grow shorter, so that the most 



