24 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
ventrals may exist in three different conditions of union; they may 
simply overlap, as in Ovecosteus ; they may be fused into a single elon- 
gated piece; or they may be interlocked with one another, Examples 
of these three modes of union will now be considered,* 
Interlocking Median Ventrals. — Two instances have been recorded 
where the median ventral plates of Dinichthys are articulated with one 
another; the first was made known by E. W. Claypole in 1893,” the 
second by the present writer in 1896.° In both cases the plates oc- 
curred in the detached condition, and were referred provisionally to 
the genus Titanichthys. Further investigation has since shown this to 
have been an erroneous determination, and the only genus that they 
can be certainly referred to in the present state of our knowledge is 
Dinichthys. The original of Professor Claypole’s figure is preserved in 
the Museum of the Ohio State University at Columbus. It is a very 
large and heavy postero-ventro-median, and with it were associated the 
greater part of the postero-ventro-laterals. The proportions indicate a 
considerably larger species than either D. terrelli or D. hertzert, and 
accordingly the name D, ingens* has been suggested for it by A. A. 
Wright. As a detailed description of these remains is in course of 
preparation by Professor Wright, it is sufficient for our purpose merely 
to cite this as an illustration of a particular mode of union between the 
median ventrals. 
The other example of articulation or dovetailing is furnished by a speci- 
men in the Museum of Comparative Zoölogy, now figured for the first 
time (Plate 2, Fig. 2). It is broadly lozenge-shaped, and its diagonals 
measure 20 by 31 cm. The resemblance of this plate to the posterior 
part of the single element in D. terrelli, already referred to, as figured 
by Newberry and Dean, is obvious. Its size, thickness, and markings im- 
pressed upon it by the paired ventrals, are also in substantial agreement. 
In these particulars it is seen to be closely allied to D. terrelli ; but on 
the other hand the articulation with the antero-ventro-median is precisely 
the same as in D. ingens. The plate in question was collected by Mr. 
Terrell, in the Cleveland Shale of Lorain County, Ohio; but whether 
1 See abstract of a preliminary paper by A. A. Wright, entitled, “New Evi- 
dence upon the Structure of Dinichthys ” (5th Ann, Rep. Ohio State Acad. Sci., 
1897, pp. 59, 60). 
2 Report Geol. Survey of Ohio, Vol. VII. p. 611, Plate XL. Fig. 1. 
8 Amer. Journ. Science, [4], Vol. IL p. 47. 
4 Should an identity be established between these plates and the mandible 
described by Claypole as D. kepleri, the latter name is entitled to priority. 
