22 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



regarding the structure of the plastron should have received important 

 modifications in consequence of later discoveries. Thus, Newberry's 

 supposed posterior ventrals were afterwards identified as the suborbitals, 

 and his so called "jugulars" have since been demonstrated by Wright^ 

 to be in reality the posterior ventrals. 



The restorations of Wright and Dean^ (the latter being somewhat 

 modified after Wright's figures) leave the median plate or plates un- 

 accounted for, and it remained for Dean in a subsequent publication ^ 

 to reconstruct the ventral covering afresh, with the addition of a single 

 element along the median line. But as pointed out by the present 

 writer in a review of Dean's article,* the evidence is not entirely con- 

 clusive that a distinct antero-median ventral was not present in advance 

 of the posterior element and overlying it, although now obscured on the 

 specimen by weathering. The writer has since had an opportunity for 

 examining the original, which is referred by Dr. Dean with some hesita- 

 tion to Binichthys gouldi. Although it is badly fractured precisely at 

 the spot where we should expect a suture to exist, and therefore in- 

 capable of affording positive proof on this point, nevertheless the fact 

 that the two plates we know were at least potentially present should 

 have retained their normal position with respect to each other, while 

 the adjacent plates have become displaced, points strongly toward a 

 union of some kind between them. 



For an undoubted example of fusion of the mid-ventrals we must turn to 

 the specimen of Dlnichthys terrelU figured by Newbeny on Chart VI. 

 (Fii^ure A), accompanying the second volume of the Ohio Geological Sur- 

 vey Report. The original is still preserved in the School of Mines Cab- 

 inet, and has been recently refigured by Dr. Dean.^ The resemblance of 

 the anterior and posterior portions to plates presently to be described, 

 and occurring as distinct elements, is sufficiently obvious. In this speci- 

 men, and the statement doubtless applies to all adult individuals of the 

 same species, fusion exists between the mid-ventrals ; in D. gouldi fusion 

 probably likewise exists. These two instances are sufficient, in Dr. Dean's 

 estimation, to compel us "to accept the thesis that the median ventral 



1 Wrisht, A. A., The Ventral Armor of Dinichthys (Amer. GeoL, Vol. XIV. 

 pp. 313-320). 1894. Report Ohio Geol. Survey, Vol. VII. pp. 620-626, 1893. 



2 Dean, B., Fishes, Living and Fossil, 180.5, Fig. 135, p. 134. 



3 Dean, B., The Ventral Armoring of Dinichthys, etc. (Trans. N. Y. Acad. 

 Sci., Vol. XV. pp. 157-16.3, May, 1896). 



* Amer. Geol., Vol. XVIIL pp. 316, 317, 1806. 



s Dean, B., Trans. N. Y. Acad. Sci., VoL XVI. Plate III., 1897. 



