20 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
same specimen has already been published by E. W. Claypole.! Inas- 
much as this cranium lacks the marginal and suborbital plates, these 
have been supplied in the diagram from Newberry’s restoration, The 
fact that they are shown more in projection than perspective imparts a 
wider and more flattened appearance to the cranium than is strictly nat- 
ural; the dorso-laterals are likewise drawn as if flattened out, instead of 
conforming to the curvature of the body. The outline of the dorso-median 
has been reduced to scale from a photograph of an exceptionally perfect 
plate obtained from Dr. William Clark by the British Museum ; its exact 
position as regards the dorso-laterals has been ascertained from speci- 
mens in the Museum of Comparative Zoölogy. Hence the restoration 
can be considered as such only in the sense that the parts are now 
brought together in their completeness and proper relationships, and 
are shown on the same scale. 
The earlier restorations already referred to are subject to the following 
criticisms. First, the anterior portion of the dorso-median is produced 
in imagination so as to cover the exposed space behind the occipital 
region ; secondly, the conditions of overlap and underlap are represented 
on only one side of the antero-dorso-lateral, instead of on three sides ; 
thirdly, the postero-dorso-lateral is not shown at all. 
Hitherto the postero-dorso-lateral has never been found in direct 
association with other plates, and its position has accordingly remained 
in doubt. It has long been known under Newberry’s designation of 
“post-clavicular,” and is a plate of not uncommon occurrence in the 
detached condition. Its triangular form, the markings impressed upon 
it by overlying plates, and the course of the sensory canal system 
across it, appeared to the writer? sufficient evidence for assigning the 
plate theoretically to the position indicated in the diagram ; and it is 
therefore interesting to record the discovery of a specimen which estab- 
lishes the entire correctness of this inference. The new specimen repre- 
sents the right antero- and postero-dorso-lateral plates of D. terrelli, 
firmly articulated together, as shown in Plate 2, Fig. 1. It is from 
the Cleveland Shale, and was found in the vicinity of Lindale, Ohio, by 
Mr. Prentis Clark. The inner surface of the plates is alone visible, the 
external side being embedded in the matrix. The mode of articulation 
between the two plates is by pegs and sockets, the position of which is 
fairly constant among the specimens that have been observed. The lar- 
1 Claypole, E. W., The Head of Dinichthys (Amer. Geol., Vol. X. p. 199), 
October, 1892. 
2 Amer. Journ. Science, [4], Vol. II. p. 48, July, 1896. 
