"""lioK"'] PROCEEDINGS OF THE NATIONAL MUSEUM. 449 



Ctenacanthus amblyxiphias, sp. nov. Fif^. :5. 



8piiie eloni^ah^, but little curved, moderately compressed; the pos- 

 terior face with a Hat median plane bounded by a shallow jjroove on 

 each side. The ridges are wider than their interspaces, and they jjradu- 

 ally become smaller posteriorly, So as to be half the diameter of the an- 

 terior ribs. The anterior border consists of a single rib of twice the 

 diameter of the largest lateral ribs. Its front surfa<;e is smooth ; the 

 sides are marked with shallow grooves directed downward, and the 

 border is serrate with subacute tubercles, which point backward. The 

 tubercles of the ribs are closely placed and vary from round to trans- 

 verse in shape, and have a tinely grooved surface. The line of the pos- 

 terior hooks is tlush with the sides of the spine. They are small, 

 decurved, and subacute. 



The apex of the spine is wanting, so I can not give its length with cer- 

 tainty. It was probably about lOi inches. Measurements: Length of 

 fragment, 100 millimeters; length of base presented (at front), 42 milli- 

 meters; diameters at middle, anteroposterior, 28 millimeters; trans- 

 verse, 17 millimeters; transverse diameter of spine 140 millimeters, 

 from base of fore surface 11 millimeters. 



The Permian forinatiou of Texas; W. F. Cummins. 



III. — On the Cranial Structure of Macropetaliciithys. 



The typical specimen of the Macropetalichthi/s rapheidolabis Owen 

 remains one of the best for the elucidation of the type of fishes which 

 it represents, although it is very imi)erfect. It has the advantage of 

 having lost most of the surface of the cranial ossiticatiou, so that its 

 true stru(;ture is the more easily determined. The cavities of the 

 (•ranium are occupied by the Corniferous limestone, which formation is 

 its proper horizon, and one of the orbits contains a characteristic 

 brachioi»odous mollusc. The extremity of the muzzle is broken away 

 oblicpiely, and the (?) maxillary region of the right; side is lost. The 

 matrix has been si)lit from the inferior surface so as to show much of 

 the structure of the latter. 



The orbits are much in advance of the line dividing the sui)erior head- 

 shield transversely into equal halves. There are no distinct indications 

 of tlu> existence of hyomandibular supports of a lower jaw. There are 

 unsymmetrical transverse sections of hollow rods, which Ibrm area*, im- 

 mediately behind the position of the orbit on the inferior fractured sur- 

 face of the specimen. The fractured surfaces are suboval, and have 

 ditVerent directions of their long axes, owing probably to ditferent 

 directions of pressure. This they would be liable to from the extreme 

 tenuity of their walls. It is probable that this genus had a lower 

 Jaw. As to the ui)per Jaw, this was probably present also, but whether 

 it l)elongs to the palatopterygoid ar(;li or to the maxiUary can not bo 

 rroc. N. 31. 01 20 



