346 RAMSAY H. TRAQUAIR ON THE 
and accordingly he separated Platysomus macrurus as the type of a distinct 
genus Hurysomus. More than this, he described two entirely new though closely 
allied genera, Amphicentrum and Mesolepis, in the former of which the dentition 
is entirely peculiar, while in the latter the teeth somewhat resemble those of 
Eurysomus, consisting of blunted cones with constricted necks. Though not 
correct in all his osteological details, Professor Youne clearly showed that these 
genera, in spite of the differences in their dentition, are naturally related to each 
other, and that Hurynotus also cannot be disassociated from them, notwith- 
standing the more paleoniscoid aspect of its scales. Unable to include these 
forms in the Pycnodontide proper, he proposed to class them, along with that 
family, in a new “suborder,” which should be equivalent to the suborders 
Crossopterygidz: and Lepidosteide, established a few years previously by 
Professor Huxtey. To this suborder he gave the name ‘“ Lepidopleuride,” its 
principal, and indeed only tangible character being the mode of articulation of 
the scales “by strong ribs traversing their anterior margin internally,” a 
character nevertheless absent in Hurynotus. According to Dr Youne, this 
suborder included five families which he tabulated as below :— 
I—VENTRAL FIN WANTING. 
PLATYSOMIDA.—Teeth uniserial, conical, sharp. Palate bones edentulous. 
—Platysomus, Agassiz, partim. 
AMPHICENTRID&.—Dorsal and ventral margins sharply acuminated. Teeth 
in the form of tuberculated plates on the maxillary, mandibular, and palato- 
vomerine bones. Premaxillary edentulous.—A mphicentrum. 
Eurysomip&.—Teeth in the form of blunted cones on a peduncle with a 
constricted neck.—EKurysomus (= Platysomus, Agassiz, partim). 
Il.—VENTRAL FIN PRESENT. 
MESOLEPIDA.—Teeth similar to those of Eurysomus.—Mesolepis, na. g.; 
Eurynotus, Agassiz. : 
Pycnopontip£,.— Teeth oval, hemispherical, or, if elongate, blunted cones.— 
Pycnodus, Mesodon, Gyrodus, &c. (except the Labroid forms of Cocchi). 
Tetragonolepis is here excluded, as its place “is undoubtedly among the 
Lepidosteide.” 
Professor Youna’s views have in their turn met with very general adoption 
so far as the institution of the suborder Lepidopleuride is concerned. 
Dr Livrxen, for instance, in his excellent treatise on the “ Limits and Classifica- 
