28 ILLINOIS BIOLOGICAL MONOGRAPHS [198 



Some of the likenesses between Ophidon and Scorpionichthys are, — 



1. Dorsally, both skulls are flattened and have similar temporal 

 fossae. 



2. The sphenotic and the frontal bones form the posterior edge of 

 the orbit, 



3. The prootic arcade and the location of the formina are identical 

 in both. 



4. The alisphenoid and the parasphenoid are alike, with the exception 

 of a small partition between the dorso-lateral processes of the para- 

 sphenoid in Scorpionichthys- 



5. Except for the longer premaxillary in Ophidon, the maxilla and 

 the premaxillary are alike in both species. 



6. The pterygoids, symplectic, and quadrate are alike in every 

 respect. 



7. In Ophidon, canine and villiform teeth are present and only 

 villiform in Scorpionichthys, but in the latter the inner row of mandibu- 

 lar teeth is better developed. 



