36 Evolution and Distribution of Fishes 



ing Pterygotus problematicus^ occur in a cement in which 

 varying proportions of carbonate of lime, phosphate of lime, 

 iron-oxide, and bitumen are disseminated." The writer 

 has cited the above as being one of the earliest descriptions 

 of some of the most ancient fish beds, and also as referring 

 to peculiarities that will be treated of later, 



Rohon says (6/ : 4) in his paper entitled: "Die obersil- 

 urischen Fische von Oesel" that the beds are divisible 

 into two zones, a lower or Wenlock, and an upper or 

 Ludlow. The former shows no fish remains. The latter^ — 

 which is again subdivided into two zones — shows in one of 

 these abundant animal remains. Alike at Rotzikiill near 

 Kielkond, in strata known as "Wita-steinbruch," also at 

 Wesiko and Hoheneichen, some strata are charged with 

 fossilized animals that include Ceratiocaris nottingi, 

 Eiirypterus fischeri, Pterygotus osiUensis^ Bunodes lunula 

 and rugosus^ also in one or other of the above localities, 

 and in association with the above or related types, a rich 

 variety and quantity of such primitive fish-genera as 

 Thyestes, {Auchenaspis) , Tremataspis,, Coelolepis, The- 

 lodus (Pachylepis), Oniscolepis, etc. The delicate details 

 of sculpturing on the exoskeletal plates of these, prove 

 that they must have been quickly and perfectly preserved 

 after death. The "Wita-steinbruch" of Rotzikiill he de- 

 scribes as a very uniformly stratified, fine-grained, yellow- 

 white dolomite, which readily absorbs water, but when dry 

 Is very hard and breaks under hammer-blows into irregular 

 pieces of different size and form. One naturally asks then 

 as to the nature and mode of origin of such rock-strata. 



Beds described by Traquair, and which the writer has 

 examined near Loanhead, Edinburgh; also the celebrated 

 Solenhofen and Eichstadt slate deposits, with others in 

 Russia, Australia and elsewhere all closely agree in texture, 

 and in their abundant fish fauna. The usually exquisite 

 state of preservation of the fossils, not least of the fishes, 

 has often been commented on. 



While in some cases, as with the Downton bone beds, the 

 fish remains are piled together in confused masses, in many 

 instances the animals are preserved entire, and are of all 

 sizes from two or three inches up to as many feet. 



