FAUNE DU CALCAIRE CARBONIFERE DE LA BELGIQUE. 
15 
Family PLATYSOMIDÆ. 
Body more or less deep ; scales of the flank higher than broadwith largely developed articulai* 
spine, and with the keel of the inner aspect usually coincident with the anterior margin. Fins 
fulcrated; dorsal with elongated base, fringe-like posterively and extending to the commencement of 
the upper lobe of the caudal , which is completely heierocercal, and deeply clefl. Shoulder-girdle 
with infraclavicular plates. Hyomandibular suspensorium vertical or inclined slightly forwards helow. 
Gape moderale; maxilla more or less triangular in form; branchiostegal ray s in the form of narrow 
Hat, imbricating plates. Vertébral axis notochordal ; the vertébral arches and inlerspinous hones ossi- 
fied; the interspinous hones form a double sériés, upper and lower, at least in the case of the dorsal. 
The dentition varies much in different généra; heing sometimes in the form of small sharp 
eonical teeth (Plalysomusj-, of obtusely conical tuhercles projections (Amphicentrum) ; ofrounded 
obtuse teeth with constricted hase ( Eurysomus, Mesolepis), or without constricted base ( Eury- 
notas)-, in olhers, the dentition is as yet unknown ( Wardichthys, Benedenius). 
The fishes I include in this family were classified by Agassiz in the Lepidoïdei iieterocerci; hy 
Sir Philip Grey-Egerton (with the exception of Eury notas) among the Pycnodonts; while hy 
Prof. 1. Young they were included in his suborder of LEPJDOPLEURIDÆ, which he divided 
into five families,— Platysomidæ, Ampiiicentridæ, Eurysomidæ, Mesolepidæ and Pycnodontidæ. 
As, however, in many important points of general structure, they are closely allied to the Palæo- 
niscidæ while they resemble thetrue Pycnodonts in little, save the deep form of the body and the 
prévalent mode of articulation of the scales, I hâve, in the recently published fîrst part of my 
monography on British carhoniferous fishes, proposed to include the Platysomidæ, along with the 
Palæoniscidæ, Chondrosteidæ, etc., in the Acipenseroid subdivision of the Ganoids. Remarkable as 
are the différences in dentition, which the forais here included display among themselves, yet so 
closely are they linked together by other points of structure, that 1 am meanwhile inclined to consider 
these différences as heing only of « subfamily » importance. 
The Platysomidæ hâve hitherto been discovered only in rocks of Carhoniferous and Permian âge. 
BENEDENIUS, Gen. nov„ Ii . it . Traquai r ('). 
Body ovoid; dorsal and ventral lines pretty everly arched. Dorsal fin comparativelv short, 
arising considerably behind the middle of the hack; caudal powerfully heterocercal, inequilobate; 
anal short, triangular, acuminate; ventrals placed far back. A sériés of large and prominent 
médian scales extends from the front of the dorsal fin to midway between the commencement of 
that fin and the occiput; the belly between the ventrals and the lower extremity of the shoulder- 
girdle displays a sériés of prominent narrow plates, whose long axes are directed downwards and 
forwards. The scales of the rest of the body are moderate, those of the flank heing not much higher 
than hroad. Dentition unknown. 
(<) N’ayant p*s à ma disposition les matériaux nécessaires pour comparer et pour décrire convenablement le 
poisson que M. P.-J. Van Beneden a fait connaître et qu’il a eu la bonté de me prêter, j’ai eu recours à l’obligeance 
de mon confrère et ami M. le D r R.-H. Traquair, d’Edimbourg, dont le nom fait autorité dans la science. Le 
savant conservateur du Musée d’histoire naturelle d’Edimbourg a bien voulu se charger d’examiner ce poisson, d’en 
faire la description et de rechercher la place qu’il doit occuper dans la méthode. 11 m’a communiqué en même temps 
la définition de la famille naturelle à laquelle il appartient. 
Ne voulant en rien altérer les observations dont je lui suis redevable, ni en diminuer l’intérêt, j’ai pensé qu’il 
convenait de les reproduire dans la langue même dans laquelle elles ont été rédigées; mais, afin de satisfaire à 
toutes les exigences, j’en ai fait, une traduction française que je me suis efforcé de rendre aussi exacte que possible. 
L.-G. de Ko.ninck. 
