1) Class 2) Subclass crossopterygii 
• (n. pl.) An order of ganoid fishes including among living species the bichir (Polypterus). See Brachioganoidei.
Crossopterygii (lobe-finned fish) are bony fish whose fins are supported on fleshy lobes. Lobe-finned fish appeared during the Silurian period (roughly 420 million years ago). The Coelacanth and the extinct Rhipidistians are examples of lobe-finned fish. 
Cros·sop`te·ryg'i·i noun plural [ New Latin , from Greek ......... tassels, a fringe + ..............., dim. of ............ wing, fin.] (Zoology) An order of ganoid fishes including among living species the bichir ( Polypterus ). See Brachioganoidei . 
The Crossopterygii is a division of fish known as the lung fishes. They have a single or double lung, and a modified heart and vascular system. They live in shallow fresh water where oxygen levels are insufficient for gills.
[n] - fishes having paired fins resembling limbs and regarded as ancestral to amphibians
subclass Crossopterygii noun fishes having paired fins resembling limbs and regarded as ancestral to amphibians