The Ganoids 



33 



to have the "mandibular ramus without or with a reduced 

 fissure of the dental foramen, and without the groove con- 

 tinuous with it in Lepisosteus. One series of large teeth, with 

 small ones external to them on the dentary bone." Most of 

 the fossil forms belong to Clastes, but the genus shows no differ- 

 ence of importance which will distinguish it from the ordinary 

 garpike. 



Order Halecomorphi. To this order belong the allies, living 

 or extinct, of the bowfin (Amid), having for the most part 

 cycloid scales and vertebras approaching those of ordinary 



FIG. 24. Lower jaw of Amia calva Linnseus, showing the gular plate. 



fishes. The resemblance to the Isospondyli, or herring group, 

 is indicated in the name (Halec, a herring; ftopcp??, form). The 

 notochord is persistent, the vertebrae variously ossified. The 

 opercles are always complete. The branchiostegals are broad 

 and there is always a gular plate. The teeth are pointed, usually 

 strong. There is no infraclavicle. Fulcra are present or 

 absent. The supports of the dorsal and anal are equal in num- 

 ber to the rays. Tail heterocercal. Scales thin, mostly cycloid, 

 but bony at base, not jointed with each other. Mandible com- 

 plex, with well-developed splenial rising into a coronoid process, 

 which is completed by a distinct coronoid bone. Pectoral fin 

 with more than five actinosts ; scales ganoid or cycloid. In the 

 living forms the air-bladder is connected with the oesophagus 

 through life; optic chiasma present; intestine with a spiral 

 valve. /This group corresponds to the Amioidei of Liitken 

 "-3 



