2 Mr. A. S. Woodward on some 



tions of Quenstedt *, Zittel f, and others, the osteology of 

 these fishes is still very incompletely known ; and a much 

 fuller knowledge is required before the problem of their 

 relationships can be solved. One disadvantage under which 

 nearly all authors hitherto have laboured is the crushed 

 nature of the specimens. With perhaps only two exceptions^, 

 all the important Pycnodont remains as yet described are 

 flattened in the hard matrix of such formations as the Litho- 

 graphic Stone of Bavaria and France, the English Purbeck 

 Stone, and the fissile Cretaceous limestone of Mount Lebanon. 

 Such specimens are admirable as displaying the trunk and 

 fins, but rarely of much service in the matter of cranial 

 osteology; and this must be thoroughly understood before 

 there can be further progress in classification. 



A new departure can now be made by the fortunate dis- 

 covery of some beautiful skulls and other remains in the soft 

 clay of Oxfordi an age in the neighbourhood of Peterborough. 

 Thanks to the skill and care of Mr. Alfred N. Leeds, F.G.S., 

 who has already unearthed so many new Jurassic Vertebrata 

 in this formation and locality, no less than five important 

 specimens of the Pycnodont genus Mesturus are available for 

 study. Though partly in concretionary clay, they are nearly 

 all free from matrix, and can thus be examined almost as 

 readily as the bones of a recent fish ; the only difficulty con- 

 sists in imperfections and fractures due to the circumstances 

 of preservation. Except one specimen, which has been ac- 

 quired by the British Museum, these fossils are in the private 

 collection of Mr. Leeds, and will be referred to under their 

 catalogue-numbers as follows : — 



No. 1 (Leeds Catalogue). — Greater portion of head and 



squamation of abdominal region, with remains of 



paired fins. (PI. I.) 

 No. 2 (Leeds Catalogue). — Hinder portion of head, with 



fragments of squamation and caudal fin, and detached 



mandible. (PI. III. fig. 2.) 

 No. 23 (Leeds Catalogue). — Imperfect head, with jaws and 



remains of anterior squamation. 

 No. 24 (Leeds Catalogue) . — Remains of head and pectoral 



arch, several elements being detached. (PI. II.) 

 No. P. 6834 (British Museum Catalogue) . — Several isolated 



bones of one skull, comprising the parasphenoid, 



* F. A. Quenstedt, 'Handbuch der Petrefaktenkunde ' (ed. ], 1852, 

 ed. 2, 1867, ed. 3, 1883), and < Der Jura ' (1858). 



t K. A. von Zittel, ' Handbuch der PalaBontologie,' vol. iii. (1887). 



\ Mesodon rugulosm (Ag.), A. S. Woodward, Proc. Geol. Assoc, 

 vol. xii. (1892) p. 238, pi. iv. tigs. 2-4. Anomasodus Willetti, A. S. 

 Woodward, Geol. Mag. [3] vol. x. (1893) p. 489, pi. xvii. fig. 1. 



