50 



NEW EVIDENCE UPON THE STRUCTURE 

 OF DINICHTHYS. 



ALBERT A. WRIGHT. 



[ABSTRACT.] 



A restoration of the ventral armor of this fossil fish from 

 the Ohio Black Shale was described in a paper before the 

 Academy in 1894. In that paper, however, the median 

 ventral plates were not discussed, for lack of sufficient evi- 

 dence concerning their structure. The present paper is a 

 review of the evidence up to the present time, contributed 

 by various writers, concerning the median elements of the 

 ventral armor. 



There must have been either a single elongated median 

 plate, filling up the space between the lateral plates, or else 

 two plates, an anterior and a posterior median. In favor of 

 the single plate there are two specimens, ist, the large D. 

 Terrelli, figured by Dr. Newberry in the chart accompany- 

 ing Vol. II of the Palaeontology of Ohio: 2d, a small D. 

 Gouldi (.'^) described by Dr. Bashford Dean in the Trans- 

 actions of the New York Academy of Sciences, 1896. The 

 first specimen alluded to has been destroyed by fire.* The 

 second specimen is quite defective in its preservation of the 

 anterior portion, and may possibly not be irreconcilable with 

 the belief that there were two medians. In favor of the 

 theory that there were two medians there is ist, the example 

 of Coccostetis dccipicns, described by Dr. Traquair of Edin- 

 burgh, m which the arrangement of all the other ventral 

 plates is almost coincident with that in Dinichthys : 2d, the 

 example of litanichthys^ a close ally of Dinichthys^ in the 

 Agassiz museum at Cambridge, Mass., figured by Dr. C. R. 



*Siiicc this pajwr was read this specimen has been brouglit to lipht airain by 

 Dr. Dean from the Columbia collcf^e museum, showing- that it fortunately did not 

 suffer the fate of its associated plates in the Elyria fire. A new and carefully drawn 

 lig-ure of it is published in the Transactions of the New York Academy of Sciences, 

 Vol. XVI, PI. HI, coulirminy the absence of any sutural joint. 



