FAUNE DU CALCAIRE CARBONIFÈRE DE LA BELGIQUE. 
18 
Family PLATYSOxMlDÆ. 
Body more or less deep ; scales of the flank higher than broad with largely developed articular 
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 défi. Shoulder-girdle 
with infraclavicular plates. Hyomandibular suspensorium vertical or inclined slightly forwards below. 
Gape modéra te; maxilla more or less triangular in forai; branchiostegal ray s in the form of narrow 
Hat, imbricaling plates. Vertébral axis notochordal ; the vertébral arches and inferspinous hones ossi- 
fied; the interspinous hones form a double sériés, upper and Iower, at least in the case of the dorsal. 
The dentition varies much in different généra; being sometimes in the form of small sharp 
eonical leelh (Platysomus') ; of obtusely conical tubercles projections (. Amphicentrum ); of rounded 
obtuse tecth with constricted hase ( Eurysomus, Mesolepis ), or without constricted hase ÇEury- 
notus ); in others, the dentition is as yet unknown ( Wardichthys , Benedenius). 
The fishes I include in this family were classified by Agassiz in the Lepidoïdei iieterocercï; by 
Sir Philip Grey-Egerton (with the exception of Eurynotas) among the Pycnodonts; while by 
Prof. J. Young they were included in his suborder of LEPIDOPLEURIDÆ, which he divided 
into fîve families,— Platysomjdæ, 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, 1 hâve, in the recently published first part of my 
monography on British carboniferous fishes, proposed to include the Plàtysomidæ, along with the 
Palæoniscidæ, Ciiondrosteidæ, 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 inclinée! to consider 
these différences as being only of « sub family » importance. 
The Plàtysomidæ hâve hilherto been discovered only in rocks of Carboniferous and Permian âge. 
BENEDENIUS, Gen. nov., R.-ll. Traquair ('). 
Body ovoid; dorsal and ventral fines pretty everly arched. Dorsal fin comparatively short, 
arising considerably behind the middle of tîie back; caudal powerfull^ heterocercal, inequilobate; 
anal short, triangular, acuminate; rentrais 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 Iower 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 being not much higher 
than broad. Dentition unknown. 
(') N’ayant p a s à ma disposition les matériaux nécessaires pour comparer et pour décrire convenablement le 
poisson que M. P.-J. Yan 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.-ïI. Traquair, d’Édimbourg, dont le nom fait autorité dans la science. Le 
savant conservateur du Musée d'histoire naturelle d’Édimbourg 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. Il 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 Komnck. 
