82 WHITE AVBS ON FOSSIL FISHES FEOM 



The only other specimen which gives any information as to the general shape and 

 proportions of the species is No. 4. In this, as in another example of about the same 

 dimensions in the Redpath Museum at Montreal, though the dorsal outline is nearly 

 straight, the contour of the abdomen seems to have been proportionately deeper and more 

 convex than it was at an earlier stage of growth, and with age the pectorals seem to 

 become much broader relatively and more robust. 



Owing partly to the large size that the species attains to and partly to the circum- 

 stance that specimens are most frequently met with in concretionary nodules, it unfor- 

 tunately happens that the adult fish is so far represented in the Sui-vey and other 

 collections accessible to the writer, either by mere fragments or at best by specimens that 

 are too imperfect to give even an approximately correct idea of the general form at this 

 stage of growth. 



The Head. — In the number, shape and relative disposition of the dermal plates 

 which constitute the external armature of the head, there is a very close resemblance 

 between Eusthenopteron and the published restorations of Tristichopterus and Osteolepis. 

 Before attempting to describe those of Eusthenopteron, however, it may be well to premise 

 that most of the specimens of E. Foordi that the writer has seen, are so much distorted or 

 abnormally compressed, in almost every direction, as to cause the same plate to assume 

 somewhat different shapes in different individuals. Owing partly to this distortion, 

 which often causes the edges of the cranial or facial plates to project, and partly to their 

 brittleness, it is almost impossible to avoid breaking the margins of these plates while 

 hammering or splitting specimens out of the rock, and it is, accordingly, seldom that 

 any of the former are found entire. 



The cranial buckler was well developed in adult examples of Eusthenopteron, but 

 there is only one specimen (No. 1) in the Survey collection in which its characters are at 

 all well shewn, and a considerable portion of its margin is broken, though the surface 

 ornamentation is beautifully preserved. In this specimen the cranial buckler is divided 

 by a transverse suture into two plates of unequal size and dissimilar shape, the one an 

 anterior, frontal or fronto-ethmoidal portion, which it will be convenient to designate as 

 the frontal plate, and the other a posterior portion, which may be called the parietal plate. 

 The frontal plate is both longer and narrower than the parietal. 



The anterior or premaxillary region of the frontal plate forms a more or less obtusely 

 pointed snou^'. whose under-margin is fringed with an outer row of recurved conical 

 teeth, two of which are of comparatively large size and the rest uniformly smaller. In 

 specimen No. 1, the exposed portions of the larger of these outer premaxillary teeth are 

 nearly four millimetres in length, while those of the smaller ones average about two. 

 A specimen not specially enumerated, which gives a good profile view of the anterior 

 termination of the head shews that the extreme tip of the upper jaw is somewhat 

 recurved and that it slightly overlapped the apex of the lower jaw. Immediately behind 

 the snout the frontal plate narrows rather abruptly inward, after which its lateral 

 maro-ins are concavely excavated on both sides and ultimately both become gently 

 convex. The posterior margin of the frontal plate is nearly straight but slightly emar- 

 ginate in the centre. In addition to the ordinary surface markings of the cranial buckler, 

 as described in the original diagnosis of the genus, from the base of the frontal plate an 



