jj TELE OS TOMES 



recent forms may be included the fringing dor- 

 sal fin, the tubular nasal opening (Fig. 149), 

 and an external gill in Polypterus (Steindach- 

 ner), EG, in the late larval stages. 



Calamoichthys is unquestionably a divergent 

 member of the stem of Polypterus ; its form, 

 becoming elongated, has acquired a general un- 

 dulatory movement ; the paired fins have accord- 

 ingly diminished in relative size, the ventral fins 



g, finally disappearing. 



Little is known of either the living or breed- 



^ ing habits of Crossopterygians : in these they 

 might naturally be expected to resemble the 



Ganoids. 



| 



Fossil Crossopterygians 



A number of the fossil kindred of Polypterus 

 "I are shown in the succeeding figures (Figs. 151- 



\ Gyroptychius and Osteolepis, Devonian genera 

 g> (Figs. 151, 152), are certainly most nearly in 



JSP the ancestral line of the recent forms. Like 

 pjj 



many sharks and fossil Dipnoans, they present 

 a heterocercal tail, a single anal fin, and a pair 

 of dorsals. The pectoral fin of Osteolepis is 

 becoming a typical archipterygium. 



Holopty chins, another Devonian form (Fig. 

 153), approaches even more closely the dipnoan 

 types : the scales are cycloidal ; its paired fins 

 IP are distinctly archipterygial ; and the caudal 



region, reduced in length, is becoming meta- 

 morphosed into the typical diphycercal form by the ten- 

 dency of the second dorsal and anal fin to coalesce with 



