454 CHARACTERS OF PALEOZOIC FISHES— COPE. 



the skull of the M. rapheiilolabiH first described. Tlie borders of the 

 muzzle are bounded on each side by a shallow lougitudiual fossa, which 

 looks outward and downward. Each is bounded on the inner inferior 

 side by a longitudinal crest which looks downwards and extends back- 

 wards and outwards. The palate between these ridges is concave from 

 side to side. The median i)ortion is filled with matrix so that the sur- 

 face and its relations with the parasphenoid can not be seen. The 

 lateral ridges are continued to below the orbit. In front of the sup- 

 posed glenoid fossa is another longitudinally oval fossa below the edge 

 of the skull. The chorda! groove and the laminar plates descending on 

 each side of it are as in the specimen first described. 



The lateral nuchal element is separated from the median, so as to 

 show that the latter has an approximately semicircular outline when 

 seen from above. Viewed from behind, the nuchal element dis{)lays an 

 obtuse median vertical keel with a shallow fossa on each side, bounded 

 by an angle on each side at the superior margin, but fading out below. 

 The vertical diameter is considerably greater relatively than in the 

 M. rapheidolahis. I suspect that the specimen belongs to the M. siilli- 

 vantii Newb. 



Returning to the 71/. rapheidolabis I observe that the anterior borders 

 of the descendiiig axial ahv are about opposite to the lateral center 

 of radiation of the lateral line tubes, or the center of the so-called 

 supratemj^oral bone. Below the anterior border of the orbit, on each 

 side of the middle line, about 7 centimetres apart, is a pair of medium- 

 sized round foramina. Exterior to these, a little anteriorly, at double 

 the space between the two median foramina, is another pair of fora- 

 mina of oval section, which look outward, forward, and downward. 

 The bony wall of the neural canal, already described, is (iuite thick. 



There is no trace of pineal foramen such as is described by Xewberry 

 in Dinichlhyida'. The sclerotica was protected, but whether by a thin 

 extension of the prefrontal and postfVontal bones or by a special ossifica- 

 tion is not determinable. The impression only remains. A considerable 

 fossa is inclosed between the descending axial plates and the lateral 

 borders of the i)osterior part of the head-shield, which opens down- 

 ward and outward. The sculpture of the surface of the skull is pre- 

 served in one or two places. It consists of round, flattened, rugose 

 tubercles of a diameter of about 2 milliuieters placed close together. 



Affinities of MacropetaHchthiis and of the Arthrodira. — It has been 

 shown by Agassiz that Coccosteus has amainlibular arch, and by New- 

 berry that this region is present in the Dinichthyida^. Traquair has 

 also shov/n that in the former genus it is connected with the cranium 

 by a suspensorium. Free elements beneath the anterior part of the 

 head-shield have been demonstrated to exist in TTomosteus by Tra<|uair, 

 which probably include a mandibular arch. The general resemblance 

 of Macropetalichthys to the Arthrodira renders it almost certain that 

 it possesses a lower jaw, and that it is a member of that order. I have 



