ON CERTAIN CROSSOPTERYGIANS. 1249' 



branches of the rami palatini also transmitted branches from the 

 internal carotids. 



If we imagine that a processus ascendens homologous with that 

 in the Teleosts {cf. Stensio, 1922 6) was developed on the para- 

 sphenoid of Dicbyonostei(,s, tliis process ought to have issued from 

 the stretch of the bone situated between the hind end and the 

 anterior border of the internal carotid canal and the arteria 

 carotis interna, and the n. palatinus facialis would thus have 

 come to run medially of it between it and the ventro-Iateral parts 

 of the basipterygoid process. 



Of the vomer nothing is preserved in the specimen. 



The arrangement and shape of the difierent bones in the jDart 

 preserved of the dei'mal cranial roof is seen in text-fig. 3. The 

 bones were described by me in 1918, and especially later in 

 connection with my account of the Coelacanthids from the 

 Triassic of Spitzbergen, and I have here nothing of interest to- 

 add to these desci-iptions (Stensio, 1918 6, pp. 116-118; 1921, 

 pp. 133-134). 



In the present state of preservation of the fish the external 

 nasal aperture is bounded dii'ectly on the dorsal side by the 

 two anterior nasal elements and a i-ostral, while the external 

 boundary of the internal nasal aperture is probably formed by 

 the premaxillary and the rostral elements behind this. 



Sensory Canals of the Head. 



The infraorbital canal anastomoses on the snout with its fellow 

 of the opposite side in a well-developed ethmoidal commissure, 

 which is situated in the rostral elements. The supraorbital canal 

 traverses the dermosphenotic,, the lateral part of the frontal, and 

 the three nasal elements, from the anterior one of which it enters 

 the rostral plate situated next to the median line, there anasto- 

 mosing with the infraorbital canal. The exact course of the 

 supraorbital canal is clearly seen in text-fig. 3. 



Of the number of sensory canal organs and tubuli nothing is 

 known so far. 



As we shall see from the subsequent description, the sensory 

 canals on the snout in Porolepsis run exactly like those 

 in Dictyonosteus. 



EusTHENOPTERON FORM Whiteaves. 



The material of this fish at my disposal consists of two small 

 specimens collected by Professor P. D. Quensel, Stockholm, 

 during his journey to Canada, in 1913, and which were kindly 

 presented to the Paleeontological Institution at Upsala. 



The two specimens are well preserved with regard to the 

 dermal bones, but exhibit on the other hand hardly anything of 

 the primordial neurocranium. My account of this below is 

 therefore based exclusively on the description published by 

 Bryant 1919 on the material in the Buffalo Museum. 



