506 PROCEEDINGS OE THE NATIONAL MUSEUM. voi. xxv. 



stout and long-, ruiiiiino- up to the vertebral eoluiiin at the posterior 

 part of the abdoniiiial eavity. It is tirmly held against the first haemal 

 spine. In Chu'todon iind A/)t/(/onla it is eoniposed of the first three 

 interha?mals coossified. In Ilolocentru^ it is composed of the first two. 



With the family Zeida^ (which, though perhaps related to the Cha?to- 

 donts, seems to have no close affinities with any known family) Anii- 

 gon'ia has the following characters in common: 



Posttemporals unfoi-ked; prefrontals not perforated ])y the olfactory 

 nerve; first interhaemal much enlarged, l)ordering- the posterior part 

 of abdominal cavity and reaching up to first abdominal vertebra. 



DESCRIPTION OF OSTEOLOGY. 



The occipital crest is high and declivitous; its anterior edge is thick- 

 ened to a ridge on each side, which descends in a curve and is contin- 

 uous with the pterotic ridge. 



The anterior edge of the supraoccipital and the surface of the f ront- 

 als bear sharply denticulated ridges, and all of the ])ones which ai"e 

 in contact with the skin are covered with small sharp spines. 



The auditory organ forms a protruding capsule of thin, polished 

 bone on each side. 



The supraoccipital extends forward to al)ove the middle of the eyes 

 and widely separates the posterior ends of the frontals. 



At the sides the frontals spread out fan-shaped, and rise steeply to 

 the supraoccipital. They nearly reach to the pterotic supraoccipital 

 crest posteriorly. Anteriorly they are deeply excavated for the recep- 

 tion of the ))ackward-extending process from the premaxillaries. 

 From a])ove tiie orbital space a channel runs anteriorly from each 

 frontal, and is continued on nasals to their anterior end. 



The ethmoid is very small and is in a depi'ession in the upper surface 

 of the vomer. It bears a sharp keel a])Ove. which is on a level with 

 the floor of the anterior frontal excavatioi^. 



The prefrontal is not pierced ])y the olfactory nerve; the olfactory 

 foramen is between it and the ethmoid. 



The nasal is large and curves downward at its end to the palatine, to 

 which it is securely attached. 



The vomer sends lateral wings upward from its sides, which are 

 articulated to the prefrontal. 



The parasphenoid expands laterally at the front of the prootic, and 

 bounds the lower part of the myodome. From its lower surface a 

 thin keel is developed. It extends, splint-like, over the basioccipital, 

 reaching nearly to the posterior end of that bone. 



The exoccipitals meet above and below the foramen magnum. 

 From their posterior surface wings are developed for the reception of 

 he end of the large second interneural. 



