MACROPOMA. 18] 
bones resemble those of M. mantelli, but they exhibit scarcely any external 
ornament, and the operculum (op.) especially is remarkably smooth. They most 
probably represent the young of this species. 
Horizons and Localities—Turonian zones: neighbourhood of Lewes, Sussex. 
Zone of Holaster subglobosus: Burham and Halling, Kent; Dorking, Surrey. 
Zones of Rhynchonella cuvieri to Holaster planus: Burham. Zone of Marsupites : 
Ovingdean, Brighton (C. D. Sherborn). Undetermined horizons near Guildford, 
Surrey, and at North Stoke, near Arundel, Sussex. 
2. Macropoma precursor, sp. noy. Plate XX XVIII, figs. 8—10. 
T'ype.—Imperfect head, etc.; British Museum. 
Specific Characters—Much smaller than the type species, with a relatively 
wider and shorter head. External head-bones marked with coarse reticulations, 
with little or no tubercular ornament ; operculum smooth, with a few relatively 
large tubercles of ganoine in an occasional patch. Scales ornamented with 
elongated tubercles of ganoine, and no enlarged median series ; all scales of lateral 
line thickened. 
Description of Specimens.—This species is known only by fragmentary speci- 
mens of the head and trunk, representing a fish from 30 to 40 em. in length. 
The type specimen exhibits the head from above (Pl. XXXVIII, fig. 8a) and in 
imperfect side-view (fig. 8), with remains of the air-bladder, dorsal fin, and scales. 
Other specimens display the trunk and part of the tail. 
As seen in upper view (fig. 8a) the head is very distinctly wider than that of 
the type species, both in the parietal and the rostral regions ; and the cranial roof 
exhibits only a coarse reticulation, with scarcely a trace of tubercles of ganoine. 
In side-view also (figs. 8,9) the head appears relatively short, the arched sub- 
orbital (so.) being especially deep and stout, while the upper postorbital plate 
(po.') is much deeper than wide. The last-mentioned bones are coarsely reticu- 
lated lke the cranial roof; but the large lower postorbital (displaced forwards in 
fig. 9, po.) 1s reticulated only in its deep hinder half, smooth in its tapering 
anterior portion. The mandible agrees with that of the type species, except that 
it bears no tubercular ornament; and the dentary bone (fig. 9, d.) is clearly 
toothless. 
The operculum (op.) is similar in shape to that of the type species, but is 
remarkably thin and smooth. It is ornamented only sparsely and in parts by 
relatively large tubercles (figs. 8b, 9a). The gular plate, as well seen in the type 
specimen, is marked only by a rather fine tuberculation. 
All the scales hitherto observed, both in the abdominal and in the caudal 
regions, are ornamented only with elongated hollow tubercles which are nearly 
