THE 



GEOLOGICAL MAGAZINE 



NEW SERIES. DECADE VI. VOL. IV. 



No. IX.— SEPTEMBER, 1917. 



OJEZTG-TTZTj^JL. aeticles. 



I. — Notes orr the Pycnodont Fishes. 



By Arthur Smith Woodward, LL.D., F.R.S. 



(PLATE XXIV.) 



rpHE Pycnodonts were the coral fishes of Mesozoic seas, with 

 X a deepened body, produced face, and a small mouth having 

 grasping and grinding teeth, capable of obtaining their hard-shelled 

 food from hollows and crannies. They are evidently not to be 

 regarded as closely allied to any of the typical coral fishes of Tertiary 

 and existing seas, which are spiny-finned teleosteans. They are 

 merely Zejpidotus-like and Dapednis-like forms with adaptations to 

 a similar mode of life. The study of their skeleton is therefore of 

 great interest. 



A complete summary of the osteology of the Pycnodonts, so far as 

 known, was published in 1895-6 l ; and, following the observations 

 of other authors, 2 I have since had many opportunities of pursuing 

 the subject further. A detailed study of Microdon radiatus in the 

 forthcoming part of the Monograph of Wealden and Purbeck Pishes 

 for the Palseontographical Society has especially led me to review 

 the whole group of Pycnodonts, and I now venture to publish a few 

 supplementary notes which these researches have suggested. 



The normal arrangement of the roof -bones in a Pycnodont skull 

 is shown in the accompanying restoration of Mesodon (p. 386). An 

 elongated unpaired plate — the so-called supraoccipital (s.occ.) — forms 

 the median ridge behind, and completely separates a pair of plates 

 which are commonly identified as parietals (pa.). Each of the latter 

 seems to represent a true parietal fused with a supratemporal ; for 

 in Microdon radiatus, at least, it is clearly traversed behind by two 

 parallel transverse slime-canals. The bone also bears at the middle 

 of its hinder border a smooth process with digitate end, which passes 



1 A. S. Woodward, Catalogue of Fossil Fishes in the British Museum, 

 pt. iii (1895), pp. 190-8 ; also " On some Remains of the Pycnodont Fish, 

 Mesturus, discovered by Alfred N. Leeds, Esq., in the Oxford Clay of 

 Peterborough": Ann. Mag. Nat. Hist. [6], vol. xvii (1896), pp. 1-15, 

 pis. i-iii. 



2 D. G. Kramberger, " De Piscibus Fossilibus Comeni, etc.": Djela 

 Jugoslav. Akad. , vol. xvi (1895), pp. 18-34, pis. v-vii, fig. 1. E. Hennig, 

 " Gyrodus und die Organisation der Pyknodonten " : Pala;ontographica, 

 vol. liii (1906), pp. 137-208, pis. x-xiii ; also " Ueber einige Pyknodonten 

 vom Libanon" : Centralbl. fur Mineral., 1907, pp. 360-71. 



DECADE VI. — VOL. IV. — NO. IX. 25 



