26 ILLINOIS BIOLOGICAL MONOGRAPHS [196 



The parasplienoid has no partition between the lateral processes to 

 separate the anterior and posterior portions and differs from Ophidon 

 in that the ventral surface of the anterior portion bears a conspicuous 

 ridge. 



The epiotic ends posteriorly in two processes. 



The condylar processes of the exoccipitals are relatively longer 

 than in Ophidon but not as long as in Scorpionichthys 



Facial Bones 



The premaxillary is relatively shorter than in Scorpionichthys and 

 much shorter than in Ophidon. Villiform teeth are present but there 

 is a modifification of these in the outer row, as they are much heavier 

 and longer than those of the inner rows. 



The maxilla has a flange on its dorsal surface where it comes in 

 contact with the first suborbital bone. Posterior to this flange the bone 

 is flattened. 



There is a facet on the anterior mesial edge of the palatine where it 

 comes in contact with the ethmoid. Only the villiform teeth are present. 

 The shank of the hyomandibular forms nearly a rectangular cross with 

 the bar which bears the facets for the anterior head and the opercular 

 bone. This causes the shank, which extends ventrally and slightly pos- 

 teriorly in Ophidon, and directly ventral in Scorpionichthys, to extend 

 antero-ventrally in this form. 



The metapterygoid has a short rounded anterior process and a 

 groove, formed by lateral and mesial flanges, on the posterior edge for 

 the shank of the hyomandibular and the hyoid artery. 



There are no particular differences shown in the quadrate except 

 that it is more anterior in this fish than in the other species described, a 

 condition brought about by the position of the hyomandibular shank. 

 The quadrate lies ventral to the anterior edge of the orbit while in 

 Ophidon it lies ventral to the posterior edge and in Scorpionichthys it is 

 ventral to the central portion of the orbit. 



The preopercular lacks barbs and spines and has no grooves nor 

 ridges. It lies postero-ventral on account of the shank of the hyomandi- 

 bular and the position of the quadrate. On this account the posterior 

 end of the suborbital stay is somewhat lower. 



No lateral ridge is present on the mandible and no cavity within the 

 dentary, nor is there a mesial flange on the ventral edge, as in Ophidon. 

 The dentary is relativ^ely much shorter than in Ophidon and somewhat 

 shorter than in Scorpionichthys. Villiform teeth are present but there 

 is a slight modification of those of the outer row. They are longer and 

 much heavier than those of the inner rows. 



