STRUCTURE AND AFFINITIES OF THE PLATYSOMID. 379 
ossified. The neural spines are succeeded above by a proximal set of inter- 
spinous bones, which in Platysomus at least extend forwards as far as the 
occiput, above which is a second or distal set supporting the rays of the dorsal 
fin. The arrangements on the hemal aspect are probably essentially similar 
as regards the presence of two sets of interspinous bones. The rays of the 
median fins exceed their supporting ossicles in number, and also overlap their 
extremities. 
This series of forms may, I think, in the present state of science, be taken as 
forming a family, for which the name Platysomide will be appropriate, as the 
genus Platysomus was not only the first known of the group, but in its structure 
the peculiarities characteristic of the series seem to have attained their greatest 
amount of specialisation. Further subdivision of the family may at present 
remain unattempted, for although distinct “subfamilies” seem certainly to be 
represented by the genera Hurynotus, Mesolepis, Cheirodus, and Platysomus, yet 
there is considerable difficulty in dealing with Benedenius and Wardichthys, 
inasmuch as their entire structure is not yet sufficiently known. 
Affinities of the Platysomide. 
It now remains for us to endeavour to ascertain the position of the Platy- 
somidee in the system, or, in other words, to inquire as to the relative amount 
of structural affinity which they betray to other groups of fishes, fossil or recent. 
Opinions of Previous Authors.—We have seen in the introduction to this 
memoir, that various opinions as to the position and classification of the genera 
here ranked as Platysomidee have been maintained by various authors, which 
opinions may now be briefly recapitulated. 
1. Aaassiz originally classed Hurynotus and Platysomus, along with Pale- 
oniscus and Amblypterus, in the Heterocercal division of his family Lepidoidei 
belonging to the order Ganoidei. 
2. GIEBEL classed the above-named forms, along with others, in his group of 
Heterocerci Monopterygii. 
_ 3. Grey-EcErton placed Platysomus in the family Pycnodontide, in which 
he also included Tetragonolepis, at the same time leaving Hwrynotus with Pale- 
oniscus in the Agassizian group of Lepidoidei Heterocerci. 
4. Voer classified Hurynotus and Platysomus along with Palconiscus in the 
subfamily Paleeoniscide of his family Monosticha, in which a second sub- 
family was constituted by the Dapediide. 
5. WAGNER placed Platysomus in his family “ Stylodontes,” in which it was 
associated with Tetragonolepis and Dapedius. . 
6. Youne divided the genera, which in this essay are taken together as 
Platysomide, into four distinct families of Platysomidw, Amphicentride, Eury- 
VOL, XXIX, PART I. 5 E 
