of Certain Body-plates in the Dinichthyids. 47 



amount of additional evidence regarding the body-covering of 

 the Dinichthvids. It is intended first to give a brief descrip- 

 tion of two plates which complete the median ventral armor of 

 Titanichtliys ; second, to locate a ^\2iiQ oi Dinichthys which 

 has been known for a long time in a more or less imperfect 

 condition, but whose exact relationships have never been 

 definitely determined ; and third, to call attention to the pecu- 

 liar " nail-head " termination of the median dorsal shield in 

 Dinichthys. The illustration of the parts presently to be 

 described, together with more detailed observations on the 

 structure of the Dinichyids, is deferred until another time. 



The material upon which the following notes are based was 

 brought together by that indefatigable collector, Mr. Jay 

 Terrell, of Oberlin, Ohio. It is all from the Cleveland Shale 

 of Lorain County, Ohio, and is now preserved in the Museum 

 of Comparative Zoology at Cambridge, Massachusetts. 



Median ventral plates of Titanichthys^ — Three perfectly 

 preserved specimens afford a complete insight into the struc- 

 ture of the median portion of the plastron in Titanichtliys^ 

 and we may assume that essentially similar elements were pres- 

 ent in Dinichthys. Heretofore only one element has been 

 provisionally assigned to the ventral surface of Titanichthys. 

 K^ewberry mentions such an one, but was disposed to regard it 

 as the equivalent in itself of the five distinct plates which con- 

 stitute the plastron of CoccosteusJ^ There can be no doubt 

 as to the identity between this plate and the one figured by 

 Claypole in Volume YII. of the Palaeontology of Ohio,f 

 which is also provisionally referred to Titanichthys. The third 

 specimen is that examined by the writer ; and it confirms Clay- 

 pole's determination of the genus, and also his identification of it 

 as a median ventral. This specimen is more perfect in outline 

 than Prof essor Clay pole's, and shows distinctly a wide impressed 

 area on the four sides of the lozenge, formed by the overlap- 

 ping margins of the anterior and posterior pair of ventrals, 

 thus proving that the plastron of Titanichthys was constructed 

 on the same general plan as in Dinichthys and Coccosteus. 



There are two unique specimens in the Terrell Collection 

 representing the anterior median ventral. The larger plate is 

 28*^°^ long, and 18^°^ wide at the base. It is perfectly symmetrical ; 

 and, as seen from the dorsal side, lanceolate in outline, and 

 traversed by a low median longitudinal ridge. This ridge 

 merges with a pair of transverse elevations of moderate size at 

 the major end of the plate, thus forming an inverted T in 



* '"Nothing corresponding to the plastron of Z>mic7ii/?i/5 and Coccosteus. cova- 

 posed of five distinct plates, has been found associated with the other bones of 

 Titanichthys, but instead, a single large triangular plate, which may have been its 

 representative." — Xeioberry, J. S.. Palaeozoic Fishes of North America (Monogr. 

 U. S. Geol. Survey, No. XYI. 1889). p. 132. 



f Plate XL, Figure 1. " Yentro-median plate? " 



