XVIII TELEOSTOMI—CROSSOPTERYGII A477 
complete, including a pair of infra-clavicles. With rare excep- 
tions the fin-rays of the median fins retain their numerical pre- 
ponderance over the supporting radials. The group is divisible 
into two “sub-orders,” the OSTEOLEPIDA and the CLapistrA.! 
Sub-Order 1. Osteolepida. 
The obtusely or acutely lobate pectoral fins articulate with the 
pectoral girdle by a single basal endoskeletal element. Nostrils 
on the ventral surface of the snout. Two dorsal fins and an 
anal fin. Dermal bones of the ethmoid region often fused with 
one another and with the premaxillae in front and the frontals 
behind to form a continuous rostral shield. Infra-dentary bones 
may be present. A series of lateral jugular plates often present 
in addition to the pair of principal plates. The Osteolepida 
first make their appearance in the Old Red Sandstone and 
Devonian formations, where they become abundant. They are 
also well represented in the Carboniferous, but only one family 
survived to the Mesozoic period, finally becoming extinct in 
the Upper Cretaceous. The following are the more important 
families :— 
Fam. 1. Osteolepidae.—Scales rhombic and thickly en- 
amelled. Pectoral and pelvic fins obtusely lobate. Tail hetero- 
cercal. Teeth simple, not complicated by surface infoldings 
TOSS EES 
Seceunee 
Fig. 273.—Restoration of Osteolepis macrolepidota. Old Red Sandstone. 
(From Traquair. ) 
except quite at the base. Genera :—Osteolepis (Fig. 2°73), 
Thursius, Diplopterus (Middle Old Red Sandstone, Scotland), 
Glyptopomus (Upper Old Red Sandstone, Scotland), Megalich- 
' Boulenger, Poissons du Bassin du Congo, Bruxelles, 1901, Pp: 2.) smith 
Woodward (Brit. Mus. Cat. Foss. Fishes, ii. 1891, p- 317; and Vert. Palaeont. 
Cambridge, 1898, p. 78), following Cope, recognises four sub-orders, the Haplistia, 
Rhipidistia, Actinistia, and Cladistia. The first sub-order is reserved for the 
Tarrasiidae, a family which includes only the little known Tarrasius problematicus 
from the Lower Carboniferous of Scotland. 
