710 Davis — On the Fossil Fish-Remainsof the Coal Measures of the British Islands. 



considers may be the intercalare or pterotic. The element in front of the parietal 

 is the cartilaginous representative of the frontal, vrhich terminates posteriorly in 

 two free processes. There are also "distinct paired membrane bones which 

 appear to represent the frontals in Ceratodiis''^ \ each is a flat, subcrescentic 

 supra- orbital plate, which has a concave superciliary border. It is separated by a 

 considerable interval from its fellow on the of)posite side. A fossa on its anterior 

 extremity is supposed to repi^esent the anterior nostril. 



The occipital bone includes ex-occipital and basi-occipital elements combined. 

 There is a prominent cup-shaped occipital condyle. The occipital extends only a 

 short distance on the inferior surface, and is attached directly and without 

 imbrication, to a continuous axial element which it is suggested is a combination of 

 the sphenoid and pre-sphenoid bones. The upper jaw, consisting of palatine and 

 pterygoid elements without division, was apparently articulated with the post- 

 orbital process of the cranium. The posterior border of the palato-pterygoid forms 

 a prominent rim descending to the mandible and forming a regular ginglymus, 

 the mandible bearing the cotylus. The mandible is robust; inferior edge thin 

 and incurving anteriorly. The superior border is regular, only rising a little in 

 the coronoid region corresponding with a concavity in the pterygoid region. A 

 portion of a hyo-mandibular bone is exposed. 



These remarkable specimens constitute the first recorded discovery of the 

 skulls of Pleur acanthus, showing that they were divided by sutures into segments, 

 and this Prof. Cope considered was a sufficient reason for the institution of a new 

 order of the Elasmobranchii, which he names the Ichtliyotomi. 



A very interesting series of specimens, between twenty and thirty in number, 

 have been found by M. Fayol in the Coal Measures of Commentry, Allier, in 

 France. These were forwarded to M. Charles Brongniart, of the Museum of 

 Natural History, Paris, and have been described and figured as Pleiiracanthus 

 Gaudryi, Brong.* They vary in length between 0"5 and I'O m., and the head 

 occupies about one-fifth the length of the fish. It is not possible, in any of the 

 specimens, to distinguish the pieces composing the head. The jaws are rounded 

 in front and furnished with small teeth along their borders. On one specimen 

 four grooves were distinguishable, probably representing the branchial arches. 

 The spine is straight, pointed, and on the upper part on each side is a row of 

 denticles, recurved towards the base of the spine, which most nearly approaches 

 P. Frosardi, Gaudry, and P. pulchellus, Davis. " Derriere I'aiquillon c^phalique 

 se dressent de petits rayons r^unis k lui par une membrane, formant ainsi une 

 nageoire que nous apiDcllerons cephaliquer This fin is stated to be similar to that 



* " :6tudes sur le terrain houiller de Commentry," Bull. Soc. de I'lndustrie Minerule, ser. 3, tome ir. 

 4ieme Livr. 1888, pis. i.-vi., woodcuts 1-15. 



