RECENT CROSSOPTERYGIAN 



149 



their isolated position, these recent forms become of ex- 

 treme interest to the morphologist, and from the side of 

 their development, when this comes to be studied, they are 

 expected to throw the greatest light on the relations of the 

 primitive Teleostome to the sharks and Dipnoans, on the 

 one hand, and to the Ganoids on the other. 



Polypterus * presents the exoskeletal characters of the 

 ancient Crossopterygians, and the typical conditions of 

 their lobate pectoral fins ; the dermal plates of its head 

 region are tuberculate as in Dipnoans, but, unlike 

 these, their arrangement, as in all Teleostomes, is dis- 



Fig. 149. — Polypterus lapradei. (After Steindachner.) Head region of 

 well-grown larva showing external gill, EG. 



tinctly paired, i.e. "ethmoids," frontals, parietals, occipi- 

 tals (Fig. 148 A), including a pair of gular plates in the 

 throat region, B.^ Among the structures peculiar to the 



* Polypterus occurs in the Nile, but is rarely taken below the Cataract. It 

 was noted, however, from near Cairo in the Description d'Egvpte, and a spec- 

 imen in the possession of Professor Innes of the College of Medicine, Cairo, was 

 taken near Bodlak a few years ago. It is known by the Arabs near Assuan, 

 and is here occasionally taken in the fykes at the beginning of the flooding- 

 season. The remarkable series of Polypterus in the Vienna collection was 

 collected in the White Nile, although some of these specimens. Dr. Stein- 

 dachner has stated personally to the writer, were taken in Middle Egypt. It 

 seems evident to the writer, from the results of his collecting-trip from Cairo 

 to Assuan, April and May, 1892, that abundant material of Polypterus is not 

 readily secured below the Second Cataract. Until, therefore, the interior of 

 Egvpt is made more accessible to foreigners, developmental stages can hardly 

 be hoped fur. 



t As in some of the fossil lung-fishes. 



