158 TRANSACTIONS OF THE [May 11, 
the endoskeletal and appendicular structures of Dinichthys 
should be discovered. For the vertebral column, girdles and fin 
structures are certainly more constant as landmarks in the dif- 
ferentiation of genera than are the outlines or tuberculations of 
_dermal or dental plates. 
It is now accordingly of general interest that a fossil has been 
found which throws unquestionable light upon the structures of 
the backbone and fin bases of Dinichthys. This unique speci- 
men* was discovered in the vicinity of Berea, Ohio, by Dr. 
William Clark, to whose zealous studies, indeed, a large part of 
our knowledge of American Arthrodirans has been due. It was 
brought to my attention in 1894 by Dr. Clark, and was subse- 
quently forwarded to the Zodlogical Laboratory of Columbia 
University for renewed study. <A further courtesy of its dis- 
coverer has now enabled me to present the following description : 
The fossil is contained in an oblong shaiy concretion, some- 
what coarser in texture—sandstone-like and lighter in color— 
than those commonly found in the Cleveland shales. It 
measures about 25 cm., occupying almost the entire length of 
the concretion. The appearance of the fossil is shown in the 
accompanying figure (Plate VII.). This,it should be explained, 
was prepared from a tracing of the structures displayed on the 
right half of the concretion, and to this drawing were added 
from the counterpart the posterior ventral plates, R PV and 
L P V, acoprolite,C, a portion of the “ventral fin,” V F, and the 
two plates of unknown position, U. These additional structures 
are accordingly shown in their normal position in the fossil, but 
the plates RPV and LP V should be understood to overlie, 
not underlie, the ventro-median plate, V M. 
As to the identification of the fossil as Dinichthys, a compari- 
son of the plates, VM, RPV, LPV and AV, with those of the 
ventral armoring of Dinichthys as figured by Newberry} and 
Wrightt leaves little doubt that these structures belonged to 
this genus. The plates are relatively thinner, however, than 
those of the types of D. terrelliand D. intermedius, but the writer 
finds by an examination of the plates of the type D. gouldi, 
Newb., preserved in the Geological Museum of Columbia, that 
the present specimen may be assigned almost definitely to this 
species. 
The fossil presents for examination the following structures : 
(A). Plates of the ventral armoring, AV, VM, LPV, RPV, 
cB G a) 
*The type is preserved in the Clark collection. __ : js 
+Newberry, Paleozoic Fishes of North America, U. S. Geol. Surv. Monogr. XVI. 
tWright, The Ventral Armor of Dinichthys, Am. Geol. Vol. XIV., Noy., 1894. 
