26 



BKITISH FOSSILS. 



affinity. I may make my meaning more intelligible by a diagi'am, 

 however. 



Paleozoic. 



Ctenododipterini, Phaneropleurini, Glyptodipierini, Saurodipterini, 

 Coalacanthini. 



j Mesozoic. I 



Codacanthini. 



Tertiaky, 



Recent. .. 

 Polypterini. 



Here it is obvious that, in time, the Polypterini are twice as 

 remote from their immediate zoological affines, the Saurodipterini 

 and Glyptodipterini, as they are from their more distant connexions, 

 the Coelacanthini. 



It seems singular that while the line of the rhombiferous 

 Crossopterygidse has so distinct a modern representative, the 

 cycliferous Crossopterygidee seem to have died and left no 

 issue at the end of the Tertiary epoch. But without wishing to 

 lay too much stress upon the fact, I may draw attention to the 

 many and singular relations which obtain between that won- 

 derful and apparently isolated fish, Lepidosiren, sole member 

 of its order, and the cycloid Glyptodipterine, Ctenododipterine, 

 Phaneropleurine, and Coelacanth Crossopterygidae. Lepidosiren 



Fig. 18. 



Diagram of Lepidosiren. (The lower figure represents the pectoral fin on a larger scale.) 



is, in fact, the only existing fish whose pectoral and ventral mem- 

 bers have a structure analogous to that of the acutely lobate, 

 paired fins of Holoptychius, of Dipterus^ or of Phaneropleuron, 

 though the fin rays and surface scales are still less developed 

 in the modern than in the ancient fish. The endoskeleton of 

 Lepidosiren, again, is, as nearly as possible, in the same condition as 

 that of Phaneropleuron, and is more nearly similar to the skeleton of 

 the Coelacanths than that of any other recent fish ; while, perhaps, it 

 is not stretching the search for analogies too far to discover in the 



