484 THE AMERICAN NATURALIST. [VoL. XXXII. 
extended along the front margin on the inner side, very similar 
to that shown in the figures of Rhynchodus given herewith 
(Figs. 45, 46). Evidently, it lodged cartilage or ligaments for 
holding the plates firmly together at the symphysis. 
From the foregoing account it will be seen that the general 
aspect of this species is suggestive of Palzomylus, which 
differs from Ptyctodus in having a much heavier and wider 
symphysial area, and is without definite tritors. That it forms 
a connecting link between these two genera we cannot doubt 
for a moment. 
(7) P. panderi, sp. nov. (Figs. 31-34).—- The type of this 
species, shown in Fig. 32, is contained in the Schultze Collec- 
tion of the Museum of Comparative Zoology, along with about 
fifteen less perfect dental plates, tritors, or detached symphyses. 
According to a MS. label in German script, these specimens 
were obtained through a collector named Kréoffges in 1859, 
and came from the Devonian of Berndorf and Gerolstein in 
the Eifel District. Evidently their description was at one time 
intended (perhaps by Hermann von Meyer, who had access to 
part of this collection), for they are marked with the MS. name 
of “ Ptyctodus pandert, n. sp.” This name may very appro- 
priately be retained and validity given to it by the following 
brief diagnosis. 
P. panderi, a species accompanying P. molaris in the Eifel 
Devonian, and related to it in the same way that P. compressus 
is to P. calceolus. Lower dental plates attaining a length of 
6 cm., but commonly not more than 4 cm., and in height about 
1.5 cm., with only a very slight sigmoidal curvature in an 
antero-posterior direction, and strongly compressed laterally. 
Outer face forms superiorly a sharp, nearly straight knife-edge 
extending from the tritoral area to the anterior beak, a distance 
of about equal length with the tritors. The cutting edge rises 
very slightly and suddenly to form the anterior projection, 
below which the anterior margin is moderately convex. Wit 
scarcely any thickening on inner face at the symphysis, and 
inferior projection at this region not observed (perhaps want- 
ing ?). Upper dental plates likewise thin and nearly rectilinear. 
This species forms with P. compressus, from which it differs 
