QiiQ On the Anatomy &c. of the Order Discocepliali. 



only at the anterior end of the latter^ capable of a certain 

 amount o£ independent movement. Palatine elongate, 

 attached by its upper edge to the lateral ethmoid ; pterygoid 

 and mesopterygoid ankylosed ; suspensorium, branchial, and 

 opercular bones otherwise typically Percoid. Skull broad, 

 very strongly depressed, with flat or concave upper surface; 

 basisphenoid and alisphenoids absent; exoccipital condyles 

 transversely expanded, wide apart ; nasal and praeorbital 

 firmly united to each other and to the lateral ethmoid ; 

 number and arrangement of other bones of skull as in the 



Fiff. 2. 



p soc ioc "epo yU:-'' opb eoc ^ -(roc pro 



Hemora clypeata. Skull from cabove (A) and below (B). 



V, vomer ; eth, mesethmoid ; leth, lateral ethmoid ; pror, praeorbital ; 

 n, nasal ; f, frontal ; ;;, parietal ; soc, supraoccipital ; ex, exocci- 

 pital ; boc, basioccipital ; epo, epiotic ; opo, opistbotic ; pto, pterotic ; 

 spo, spbenotic ; pro, prootic ; psp, paraspbenoid ; pit, post-temporal. 



Perciformes. Vertebrse 23 to 30 ; ribs and epipleurals 

 inserted together on strong transverse processes. Pectoral 

 arch of the Perciform type, except that the supraclei thrum 

 is reduced and 3 radials are in contact with the hypocora- 

 coid ; pelvic bones directly attached to the cleithra. 

 Two families may be recognized : — 



Family 1. Opisthomyzonidae. 



Disc of about 6 segments, small, narrow, not extending 

 forward to the interorbital region, its width about ^ the 

 width of head. Vertebrte 23 or 24. Dorsal fin longer than 

 anal ; caudal widely forked. 



Opisthomyzon glaronensis from the Upper Eocene of 

 Switzerland (Wettstein, Mem. schweiz. Palseont. Ges. xiii. 

 ]886, p. 82, pi. vii. fig. 10 ; Storms, Ann. & Mag. N. PI. (6) 

 ii. 1888, p. 73 ; Cope, Amer. Nat. xxiii. 1889, p. 355). 



