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NEW YORK STATE MUSEUM 



ever, is shown by a convenient fracture, although there is no evidence that 

 it terminated in a distinct process, as in Dinichthys, Ahlostoma, and other 

 genera. Measurements show that the extreme length and width of this 

 plate are very nearly equal, the distance between the anterolateral extremi- 

 ties amounting to 70 cm. In an earlier restoration of T. agassizi by 



■ation of head shield ai 

 ral ; C-central ; Z).l/=dorso 



the present writer," the dorsomedian is shown as being partly overlapped by 

 the adjacent plates on either side. This is now believed to be erroneous, 

 the relations of o\erlap are as in Dinichthys, and the idea that a carina! 

 process was present was suggested by a photograph of a plate purporting 

 to belong to T. clarki, but which, upon examination of the original, 



' Am. Nat. 1808. 32: 763, fig. 4. 



