STRUCTURE AND AFFINITIES OF THE PLATYSOMIDA. 389 
_ Final Summary. 
_ Weare now, I think, justified in concluding,— 
} 1. That the Platysomide are specialised forms, which have, if the doctrine of 
descent be true, been derived from the Paleoniscidee. Their structure presents 
us simply with a modification of the Paleeoniscoid type, and wherever the Pale- 
oniscidee are placed in the system, thither the Platysomide must follow.* 
2. The resemblances. between the Platysomidz and the Dapediide and 
Pycnodontidz are mere resemblances of analogy, and not of real affinity. The 
Dapediide are related not to the Palsoniscide or Platysomide, but to the 
other semiheterocercal Ganoids of the Jurassic era (Lepidotus, &c.), and the 
Pycnodonts are highly specialised forms, whose general affinities point in the 
same direction. 
EXPLANATION OF THE PLATES. 
Throughout these figures the same letters apply to the same bones. 
p. Parietal. sp. Splenial.. 
sq. Squamosal or dermal-pterotic. op. Operculum. 
J. Frontal. i.op. Interoperculum. 
pf. Posterior frontal or dermal-sphenotic. p.op. Preoperculum. 
af. Anterior frontalordermal-ectoethmoidal. br. Branchiostegal. 
e. Median superethmoidal. s.o. Suborbital. 
p.mex. Premaxilla. st, Supratemporal 
mz. Maxilla. n. Nasal opening. ~ 
pt. Pterygoid. or. Orbit. 
m.pt. Mesopterygoid. pt. Post-temporal. 
hm. Hyomandibular. 4 scl. Supraclavicular. 
ar, Articular. cl. Clavicle. 
ag. Angular. p.cl. Postelavicular. 
d. Dentary. i.cl. Infra-clavicular. 
Prate ILL. 
Fig. 1. Restored figure of Hurynotus erenatus, Ag. From a large suite of specimens in the 
Museum of Science and Art, Edinburgh, and other collections. 
_ Fig. 2. External surface of one of the anterior flank scales of the same species; magnified four 
diameters. Burdiehouse. 
Fig. 3. Internal or attached surface of a similar scale. 
Fig. 4. External surface of a scale from a position further back on the side of the body; mag- 
nified four diameters. West Calder. 
* T have already (Mem. Paleontogr. Soc., 1877) stated my reasons for placing the Palzoniscide 
and consequently also the Platysomide rather in the Acipenseroid than in the Lepidosteoid suborder of 
Ganoids. To reopen this question is, however, beyond the scope of the present essay. 
