278 Evolution and Distribution of Fishes 



Mention might also be made of another paper by J. W. 

 Davis on the English Yoredale rocks (205:40:614) and 

 of three by T. Atthey (206 : i : 77, 266; 9 : 249) on coal 

 seams at Newsham, as giving added detail. 



But for an exhaustive and correct interpretation of 

 details, the writer next presents statistics regarding two lists 

 of fishes, namely that of J. W. Davis "On the Fossil Fishes 

 of the Carboniferous Limestone Series of Great Britain" 

 {20y) and the Catalogue list of Prof. Young already cited. 

 Davis gives about one hundred and sixty marine species of 

 selachian and cestraciont fish, but naturally this number 

 would be considerably reduced did we know the true relation 

 of teeth and fin-spines to each other. He also records six 

 species of what he calls "ganoids," but three of these have 

 been shown to be elasmobranchs, while the other three ac- 

 cording to Woodward are unidentifiable. The writer reck- 

 ons that in Young's list are thirty species of elasmobranch 

 and thirty species of dipnoans and ganoids from purely 

 freshwater strata, also thirty species of the former group 

 that are marine. But comparative study of the thirty elasmo- 

 branchs reveals that while twelve of these are always and 

 only recorded from freshwater strata, the remaining nine- 

 teen species may come from freshwater and saltwater strata 

 alike, or are in other words anadromous.* 



The most striking difference in the two lists is the practi- 

 cally total absence of ganoids from Davis's catalogue. The 

 explanation of this difference is that all of the ganoids and 

 labyrinthodonts in Young's list are freshwater, and the 

 ganoids have remained so throughout their entire history, 

 except for a few derivative side-lines to be traced later, 

 and which in the sea became a dwindling factor. The 

 elasmobranchs of Young's list, on the other hand, include 

 both freshwater, anadromous, and marine elasmobranch 

 types. Thus of the first we might cite species like Pleura- 

 can thus [Diplodus) gibhosus, P. {Orthacanthus) cylindri- 

 cus, Gyracanthus formosus, Pleuroplax (Pleurodus) affinis, 

 P. rankini, Tristychius arcuatus, Cladodus parvus and 

 others. But species like Cladodus conicus, C. laevis, 



* The writer here uses this word — possibly in too wide or vague a sense — to indicate 

 any fish that can live in, and migrate from, either freshwater or marine environment. 



