388 Dr. A. Smith Woodward — Notes on Pycnodont Fishes. 



of them, sufficiently large to have been the premaxillary and dentary 

 teeth, have been found with a group of tritoral teeth of Acrotemnus 

 in the Chalk of Belgium. 1 Larger and stouter examples of " Anci- 

 strodus ", therefore, are probably the prehensile teeth of Pycnodont 

 jaws; 2 but the smaller examples, with translucent or transparent 

 enamel, belong to the pharyngeal dentition. 3 



In Coelodus the preoperculum is subdivided by an irregular 

 transverse suture into two portions, the lower being the larger. The 

 vertical slime-canal, which always traverses the preoperculum in 

 Pycnodonts near its anterior border, passes directly into the upper 

 portion, thus proving that it is not the operculum, as it has been 

 named by Kramberger, 4 and also by Bassani and D'Erasmo. 5 The 

 operculum in Coelodus resembles that of other typical Pycnodonts, 

 and the same bone in Stemmatodus is figured by Bassani and 

 D'Erasmo 6 as a supraclavicle. 



The ribs in Pycnodonts are comparatively short, extending not 

 more than half-way to the ventral border. Eacli bears a paired 

 laminar expansion tapering distally, as well seen in a specimen of 

 Gyrodus in the British Museum (No. P. 1623a). 



In the pectoral arch the supraclavicle has now been clearly 

 observed in Microdot! radiatus from the Purbeck Beds. Its exposed 

 upper portion, crossed by the slime-canal, is triangular in shape, and 

 its apex is situated at a short distance below the posterior process of 

 the parietal bone. 



In the typical Ifesodon (Figure on p. 386), as in most Pycnodonts, 

 the flank-scales are complete only in the lower part of the abdominal 

 region, beginning with four or five in the transverse row immediately 

 behind the pectoral arch and gradually diminishing to two or three in 

 the last row just in front of the anal fin; the uppermost scale in each 

 row tapering upwards to its riblet. In some of the earlier species 

 commonly referred to Ifesodoti, however, such as M. liassicas, the 

 scales are complete throughout nearly all the transverse rows ; and 

 I unfortunately made the mistake of representing this type of 

 squamation in my first restoration of M. macropterus,' 1 which is now 

 corrected. In those genera in which the squamation is more or less 

 nearly complete, either over the whole or the front half of the trunk, 

 the scales are less deep and more numerous than in the genera in 

 which the squamation is much reduced. 



In nearly all Pycnodonts the ventral ridge-scales occur in un- 

 interrupted series, and the small pelvic fin on each side is inserted 



1 M. Leriche, " Un Pycnodontoide aberrant du Senonien du Hainaut " : 

 Bull. Soc. Beige Geol., vol. xxv (1911), Proc.-Verb., pp. 162-8, pi. A. 



2 e.g. specimen figured by A. S. Woodward, Fossil Fishes of English 

 Chalk (Mon. Pal. Soc, 1909), pi. xxxv, fig. 8. 



3 e.g. specimen figured by A. S. Woodward, Proc. Geol. Assoc, vol. x 

 (1888), pi. i, fig. 10. 



4 D. G. Kramberger, Djela Jugoslav. Akad., vol. xvi (1S95), pp. 21, 31, 

 pis. v, vi. 



5 F. Bassani & G. D'Erasmo, " La Ittiofauna del Calcare Cretacico di 

 Capo d'Orlando presso Casbellammare (NapolH " : Mem. Soc Ital. Sci. [3], 

 vol. xvii (1912), p. 227, fig. 12. 



6 Loc cifc., p. 221, fig. 9. 



7 A. S. Woodward, Vertebrate Palaontology (1898), p. 105, fig. 74. 



