THE LOWER DEVONIAN FISHES OF GEMUNDEN. 727 



terminating behind in a prominent though rounded angle on each side. There is on 

 the dorsal surface a large median plate (m.d.) of an ovate- hexagonal shape, the anterior 

 margin being short and nearly straight, while the still shorter posterior one is acutely 

 notched. The outer tuberculated surface of this plate is well seen in PL I. fig. 1 and 

 in PI. II., while in PL IV. it is exhibited from the smooth inner aspect. Each postero- 

 lateral angle of the carapace is formed by a narrow, elongated, somewhat falciform plate 

 (p. I.), the postero-lateral or cornual, which, tapering to a sharp point in front, forms 

 most of the external margin of the shield. On the dorsal aspect of the carapace (PL 1. 

 fig. 1, PL II.) the entire contour of this plate is seen, the surface being closely covered 

 with the characteristic stellate tubercles, but on the ventral side (Plates III. and IV.) 

 only a thickened external margin is visible, except in dislocated specimens, which 

 margin is marked with wavy ridges instead of tubercles, and obliquely bevelled off just 

 at the postero-lateral angle. Internal to this peculiar thickened margin the inner 

 surface of the plate is smooth, and in entire examples of the fish it is, of course, covered 

 by the ventral plates (see PL III. on the left-hand side of the figure). The rest of 

 the dorsal surface is formed by small polygonal plates, well seen in PL II., and not so 

 distinctly in PL I. These remind us closely of the polygonal areas on the tessellated 

 surface of many Psammostean shields, and, as in these, we often find a central tubercle 

 which is larger and more prominent than the others with which the surface is closely 

 covered. Lastly, at the anterior margin of the dorsal aspect of the carapace we find a 

 few large rostral plates, also well marked in the specimen figured in PL II. ; the form 

 and number of these plates do not, however, appear to be constant in different 

 examples of the fish. 



An invariable appearance on the dorsal surface is a rounded pit on one of the plates 

 on each side at the antero-external margin, and close in front of the forwardly-directed 

 apex of the postero-lateral plate. This pit, conspicuously seen on the left side in 

 PL II., I first interpreted as an orbit, a view which I had to abandon on finding that it 

 had a non-perforated floor, which was also ornamented by the same tuberculation as the 

 rest of the surface. The explanation of this phenomenon I subsequently ascertained, as 

 will be seen further on. 



Proceeding now to the ventral side of the carapace, an admirable view of its con- 

 struction, though slightly imperfect behind, is afforded by the specimen represented in 

 PL III., of which I also give a still more reduced pen-and-ink lettered sketch in fig. 2 

 in the text, while in the restoration fig. 3 is added the information derived from other 

 specimens, especially that shown in PL V. fig. 1. 



First we may note the mouth (o.), which is terminal, being placed at the anterior 

 margin of the carapace. It is a transverse slit, the upper margin of which is formed by 

 the anterior edges of the rostral plates (r.) already mentioned, while at each outer 

 corner there is a small external labial plate (e.L), the tubercles on which are rather 

 larger than those elsewhere. The lower boundary of the oral slit is formed by the 

 •anterior margin of a broad pentagonal plate (m.), which we may call mental. Its 



