24 THE CANADIAN NATURALIST. [Vol. X. 



or ventral surface of a true Ptericlithys (as defined by Prof. Owen) 

 with one of the pectoral spines in situ. At the earliest practic- 

 able opportunity, Mr. Ells revisited the locality, and in the first 

 week of June last obtained three exquisitely preserved specimens 

 of the buckler of the same species and several fragments, also 

 some isolated scales of a GlyptoJepis. The finest example of the 

 Canadian Pterichthys collected by Mr. Ells had a large piece bro- 

 ken off the left margin when it was found, but with this exception 

 the whole of the upper surface of the helmet and buckler is finely 

 exposed (the plastron being partly covered by the matrix), and 

 the outline of the orbital opening is clearly defined. A few weeks 

 later, Mr. T. C. Weston, also of the Canadian Survey, collected 

 an additional number of fine specimens of the Pterlchthys from 

 this locality, some of which illustrate admirably the shape, sculp- 

 ture and mode of articulation of the pectoral spines. Associated 

 •with these there are, in Mr. Weston's collection, a nearly perfect 

 but badly distorted specimen of a GlyptoJepis fully seven inches 

 in length, some fragments of Psilop>hyton, and a spore case of a 

 L ep ido den dro n . 



Taken collectively, the specimens thus far obtained of the Ca- 

 nadian Ptericlithys show nearly all the characters of the helmet, 

 buckler, plastron and pectoral spines, in the most satisfactory 

 manner, but no vestiges of the tail have yet been detected, nor of 

 any of the fins other than the two pectoral spines. The nature 

 of tlie mouth and of its dentition, if it had any teeth, are un- 

 known, and the small isolated plate in the orbital cavity (the '-'os 

 dubium," of Pander, the " median" plate of Owen) has not yet 

 been observed. In the number, outlines and disposition of the 

 plates on the upper and lower surface of the head and body, 

 and in the shape and mode of articulation of the pectoral spines, 

 the Canadian fish agrees, in every essential point, with Pander's 

 well known figures of a typical Ptericlithys, but the sculpture 

 of the entire surface of the former is precisely like that of Both- 

 riolepis ornata Eichwald, which is thus described by Agassiz :* 

 " lies ornements de cette espece consistent en petits enfoncemens 

 circulaires places les uns a cote des autres et s^pares par des 

 carenes qui, par leur juxta-position, paraissent hexagonales a-peu- 

 pr^s comme les vitraux ronds des ancieunes fenetres, avec I'entou- 

 rage en plomb qui les reunit. Les creux ont a-peu-pres la gran- 



* Monographie des Poissons Fossiles du Vieux Gres Rouge, &c., p. 99. 



