64 FISH GALLERY. 



Dipnoi ; they consist of a thick, muscular, scale-covered middle 

 part, the lobe, either pointed or rounded at the end, and a fringe 

 or marginal membrane supported by closely-set fin-rays developed 

 in the skin (dermal fin-rays). The dorsal fins are two, or else 

 (e. g. Polypterus, 193, and fig. 40) consist of numerous finlets; 

 the pelvic fins are set well behind the pectorals (abdominal 

 position) . 



The cartilage of the skull in the Stylopterygian fishes is well 

 protected by dermal bones; there is no supraoccipital bone. 

 There are two or more jugular plates between the halves of the 

 mandible, and the branchiostegal rays have the form of lateral 

 jugular plates. There are a pair of infraclavicles in the shoulder 

 girdle. The known range of these fishes is from the Devonian 

 epoch to the present time. In the sole living representatives of 

 the order, Polypterus and Calamichthys, the heart has a conus 

 arteriosus provided with numerous valves ; there is a spiral valve 

 in the intestine, the spiracles are open, abdominal pores are 

 present, the air-bladder has an open duct, and the optic nerves 

 meet below the brain in the form of a cross, or 'chiasma/ The 

 principal suborders of the Stylopterygii are the Holoptychioides or 

 Khipidistia, the Ccelacanthoides or Actinistia, and the Polyteroides 

 or Cladistia. 



Holoptychioides. 

 The Holoptychioides are extinct fishes, the remains of which 

 occur mostly in rocks of Devonian and Carboniferous age. In the 

 anal fin and in each of the two dorsal fins the most internal 

 skeletal elements (axonosts) are fused into a single piece, with a 

 broad outer bend, bearing from three to six rod-like elements 

 (baseosts), which are fewer than the dermal fin-rays, and are over- 

 lapped by them. The skeleton of the pectoral fin articulates with 

 the shoulder girdle by a single basal element (unibasal fin). The 

 vertebral column has no ossified centra, or has ring-like centra. 

 The teeth have a complicated folded structure ; the nostrils are on 

 the lower surface of the snout. 



