Cope.] "Jo [March 16, 



fourth Contribution to the History of the Permian Formation of Texas. By 



E, D. Cope* 



{Read before the American Philosophical Society, March 16, 1883.) 



PISCES. 



ECTOSTEORHACHIS CICERONIUS, Sp. HOV. • 



The genua Ectosteorhachis Cope, is known up to the present time from 

 ichthyolites, which do not exhibit the interior details of the structure of 

 the skull. Several portions of crania having recently come into my hands, 

 I am able to add some important features, and a new species, which I name 

 as above. 



The base of the skull consists of ossiQed parachordals, which embrace 

 the chorda dorsalis posteriorly and are continued for a short distance 

 posteriorly as a tube. Anteriorly the chordal groove is open. Trabecular 

 not ossified. The cranial structure is an excellent illustration of a perma- 

 nent embryonic type. Above and in front of the opening for the chorda, 

 the neural canal enters the groove. The parachordals are subtriangular, 

 presenting one angle forwards, and having the internal side that bounds 

 the groove straight and longitudinally grooved. The anteroexternal side 

 is oblique and nearly straight, and is overhung by the osseous roof of the 

 skull. These characters are identical in both species. 



The E. ciceronius differs from the E. nitidus in having a narrower inter- 

 orbital region, and in the possession of small tubercles of ganoi'ne on the 

 posterior parts of the superior surface of the skull. These are seen 

 on the sides of the surface, and are quite small, not numerous, and 



*The third contribution can be found at page 447 Proceedings ot the Society 

 for 1882. 



mm* 



