372 RAMSAY H. TRAQUAIR ON THE 
Younc. Nevertheless, Messrs Hancock and Arruey have expressly recorded 
the presence of small ventrals in P. parvulus; and in a specimen of P. striatus 
in the Edinburgh Museum, traces of a ventral are certainly to be seen ; it is, at 
the same time, at least remarkable that in the immense majority of otherwise 
well-preserved specimens the fins in question are not observable. The pectorals 
are frequently well displayed, and are of moderate size. As regards the constitu- 
tion of the fins, the same type of structure seen in Hurynotus and in the — 
Paleoniscidee is here perpetuated ; the rays are closely set, imbricating in the 
fore part of the fin, divided throughout by transverse articulations, and having 
their external surfaces ganoid and sculptured. Dichotomisation of the rays 
commences towards their extremities in the longer rays on the front of each 
fin, creeping up to the middle in the shorter ones behind. I have not myself 
been able to detect the presence of fulcra. 
In describing the pectoral of P. striatus, AGassiz states that its rays “ ont 
cette apparence cornée que l’on observe dans les nageoires de beaucoup de 
poissons de Solenhofen et qui rend les articulations transversales des rayons 
imperceptibles.” I have, however, very distinctly observed the transverse 
articulations of the pectoral fin’ rays in P. gibbosus, parvulus, and tenui- 
striatus, 
The shoulder girdle (fig. 5) is well developed. The post-temporal element 
(p.t.) is a large plate, somewhat rounded-quadrate in shape, and placed im- 
mediately behind the cranial shield and above the operculum; it is usually 
conspicuous in every specimen of Platysomus, and is, no doubt, the part which, 
in previous descriptions, is usually called “ occipital crest.” The supraclavicular 
(s.c/.) is similar to that of Mesolepis and other genera; so is also the clavicle 
(c/.), although that is also rather more narrow and elongated. A small, though 
very distinct i/raclavicular plate (i.cl.) is attached to the front of the lower — 
extremity of the clavicle, but I have not seen any post-clavicular. 
In the larger and more typical species of the genus, such as P. gibbosus and 
striatus, the bones of the head are seldom clearly decipherable, so that in 
describing the osteology of this part I must follow the example of Professor 
Youne in using for that purpose the small Carboniferous species P. parvulus 
(fig. 5). Professor Youne has given a minute description of the cranial structure _ 
of this species, but after a most careful and prolonged examination of a large 
series of specimens in the collection of Mr Warp, I am unable to make my re- _ 
sults agree with his, or to reconcile them with his restored figure of the head. 
I can find no trace of the large “ supra-occipital ” which Professor Young — 
has represented as intercalated, Teleostean-like, between the parietals, and I~ 
cannot help strongly suspecting that the bone indicated, along with his parietal, — 
appertains to the large post-temporal plate, which occupies a similar position 
above the operculum. The real parietals are small plates (p.), articulating with 
