334 Dr. C. Liitken on the Limits and 



fl. The Neozoic (Eocene*) Pyc7wdonts had the seralvertebra? 

 developed, and consequently covering the notochord entirely ; 

 the dei-mal ribs, which are sometimes delicate and compli- 

 cated, never occupied more than the thoracic portion of the bodj. 



III. Third series. — The Gano'idei Crossojpteri or Polypte- 

 ridce^ represented in the present day by the genera PoJypterus 

 and Galamoiclitliys. The principal characters common to 

 these and their ancient representatives of the Devonian sys- 

 tem are the following : — 1, the absence of rays in the branchio- 

 stegal membrane, which are represented here only by two 

 gular plates ; 2, the very characteristic structure of the paired 

 fins, which are formed of a scaly stem, often of great length, 

 and bordered on each side with rays like a fringe ; 3, the very- 

 backward position of the ventral fins ; 4, the absence of the 

 so-called fulcral scales ; 5, the diphyocercal or approximately 

 heterocercal form of the tail, which is never fan-like. 



The true Polypteridcn of the existing period are the direct 

 representatives of the Pala?ozoici?Z'0??z/)o^Z^}:'^en (Devonian and 

 Carboniferous) with ossified, rhomboidal, and articulated scales 

 like those of the Lepidostei and Polypterij with a diphyocercal 

 or slightly heterocercal tail, with a double dorsal fin thrown 

 far back, with the base of the vertical fins scaly, &c. The 

 principal character which separates them from the Polypteridm 

 therefore consists in the double dorsal placed far back. These 

 are the genera Osteolepis^ Diplopterus^ Megalichthys (with 

 smooth scales), Glyptolcemus and Glypdopomus (with the scales 

 and bones of the head sculptured). 



The contemporaneous Cyclodipteridce present exactly the 

 same assemblage of characters, with one single exception — 

 that of the scales : these are ossified and enamelled, indeed, 

 and sometimes even thick and smooth or sculptured, as in the 

 preceding; but in place of the form, relative position, and 

 articulation common to the Eiiyano'idei, Pliomhodipteridce^ and 

 Polypteridce^ we find here the rounded cycloid form and the 

 imbricated superposition of the ordinary Teleostei. As among 

 the lihomhodipteridce, there are among the Cyclodipteridce a 

 smooth division {Ctejiodus, Dijiterus)^ and another with the 

 cranium and scales sculptured {Glyptolepis^ Holoptycliius^ 

 Gyroptycliius^ &c.). 



In a certain number, at least, of these Dipteridce^ whether 

 rhomboidal or cycloid, if not in all, the vertebral column 

 already possessed apparently a degree of development little, if 

 at all, inferior to that of the Polypteri of the present day ; in 



• A single species of this tribe is obtained from the Cretaceous forma- 

 tion of Lebanon. F"or further details concerning the true Pycnodonts, 

 their structure and classification, the reader will consult especially the 

 celebrated works of the late M. Ileckel. 



