202 University of Washington Publications in Biology [Vol. 2. 



Erectile. Susceptible of being raised or erected. 



Ethmoid. A median anterior bone of the skull, above the vomer. 



Exoccipitals. Two bones of the skull ; one on each side of the for- 

 amen magnum. 



Exoskeleton. Hard parts (scales, scutes, bony plates) on the sur- 

 face of the body. 



Exserted. Projecting beyond the general level, as fin rays beyond 

 the membranes. 



Extralimital. Beyond the limits (of this key). 



Eye. The diameter of the eye, called "eye" in descriptions, is meas- 

 ured lengthwise (horizontal diameter), the form of the orbit 

 not always being round. Most investigators use the greatest 

 diameter of the eye, if the latter is not circular. 



Eye in snout. The diameter of the eye is measured in the length of 

 the snout. 



Facial. Pertaining to the face. 



Falcate. Scythe-shaped, long, narrow and curved. 



Falciform. Curved, like a scythe. 



Fauna. The animals inhabiting any region, taken collectively. 



Filiform. Any thread-like, slender structure. 



Fin height. The height of a fin is the length of the longest ray. 



Fin length. The length of a fin is measured along its base unless the 

 length of the depressed fin is specified. The latter is measured 

 from its origin to the most posterior point of the fin. 



Finlets. A series of specialized fin rays, usually separate from each 

 other and occurring posteriorly to the dorsal or anal fins. 



Fontanel. An unossified space on top of the head, between the par- 

 ietals, covered with a membrane. 



Foramen. A hole or opening. 



Foramen magnum. The aperature in the posterior part of the skull 

 for the passage of the spinal cord. 



Forehead. Frontal curve of the head. 



Forficate. Deeply forked, furcate. 



Fossa (nasal). Groove in which the nostril opens, a shallow depres- 

 sion. 



Frcnum. A small piece of flesh binding the lip to the edge of the 

 jaw. 



Frontal bone. Anterior bone on the top of the head, usually paired. 



Fulcra (singular fulcrum.) Rudimentary spine-like projections ex- 

 tending on the anterior rays of the fins of the ganoid fishes. 



Furcate. Forked. 



Fusiform. Spindle-shaped, tapering toward both ends, but more 

 abruptly forward. 



