19 



surface of the cranium is thrown into wrinkles which form no regular pat- 

 tern, and which inosculate to a moderate extent, most so on the preorbital 

 region. The anterior parts of the niaxilliary and mandibular bones are 

 marked with small pit- like impressions. 



Measurements. M. 



Total length to quadrate angles measured on median 



line 170 



Length to supraoccipital border 138 



Total width posteriorly. 155 



Width at orbits , .-. . . .095 



" between orbits 021 



" at nares .062 



" between nares 030 



Long diameter of orbits 026 



Transverse diameter of occipital cotylus 012 



This cranium is much shorter and wider than that of Arehegosaurus 

 decheni, and has the orbits more anteriorly placed. 



CROSSOPTERYGIA. 

 ECTOSTEORHACHIS Cope, gen. nov. 



Tribe Grossopterygia ; family Rhombodipteridm Traquair ; sub-family 

 Saurodipterini Huxley. Pectoral and ventral fins rather acutely lobate, 

 with few or no radii on their external borders. Dorsal and anal fins un- 

 known. Scales imbricate, rhombic, smooth. G-anoine wanting from top 

 of head in specimens examined, but present on sides and inferior surfaces. 

 Coronal suture distinct. End of the muzzle covered with separate scales. 

 Distinct sub- and postorbital bones. Gular bones, an anterior azygus and 

 two laterals on each side, the posterior the shorter. Teeth acutely conic, 

 rather small ; a few large ones at the anterior part of each jaw. Verte- 

 bral centra represented by osseous rings which enclosed a notochord. 



This new genus is apparently nearly related to Megalichlhys, and in a 

 less degree to Osteolepis and Diploptei'ax. Pander, Miller and others repre- 

 sent the ventral fins of the two genera last named as not lobate, but sessile, a 

 state of things entirely different from what is observed in Ectosteorhachis. 

 The sub-division of the dermal bones of the muzzle is also rather character- 

 istic of Megaliclithys. From the latter genus it differs in the form of the 

 vertebral centra. Both Agassiz and Huxley describe those of Megaliclithys 

 as completely ossified, and as biconcave. In Ectosteorhachis they are repre- 

 sented by annular ossifications resembling somewhat those of the stegoce - 

 phalous genus Gricotus, but with a larger foramen chordce dorsalis. 



The elongate-lobate axis of the fins of this genus render it probable that 

 those of Megaliclithys present the same character. 



Ectosteorhachis nitidus Cope, sp. nov. 

 This fish is represented by several specimens, the best preserved of which 

 includes the head and body inclusive of the ventral fins. These form an 

 chthyolite nearly denuded of matrix, the inferior side being best preserved. 



