| 
L. Agassiz on the Ichthyological Fauna of Western America. 97 
cireling the mouth is deciduous, at least in specimens preserved 
in alcohol, showing that the attachment of this indurated edge is 
the same longitudinal direction throughout its thickness, so that 
the plate breaks very readily at right angles with its own greater 
diameter. 
The nostrils, two on each side as in all Cyprinidae, consist of a 
tubular opening in advance and a large crescent-shaped opening 
ind, 
The opercular apparatus and the branchiostegal rays, present 
ho peculiar characters. The branchiostegal membrane however 
unites with the skin under the chin on the anterior margin of the 
humerus, so that the branchial opening does not extend to the 
sides of the tongue bone. 
The dorsal begins opposite the insertion of the ventrals, which 
are themselves somewhat nearer to the anal than to the pectorals. 
The dorsal exteuds as far back as the anterior margin of the anal. 
It has three small rays in advance of the longest simple ray 
which is followed by ten branching rays, the last of which is 
properly a double ray. 
| these rays are deeply divided longitudinally and trans- 
versely articulated. The caudal is very powerful, and remarka- 
le for the many simple rays which it has along the base of its 
two lohes, there being seven above and seven below, gradually 
creasing, so that the longest reaches nearly half the length of 
the longest sim ple ray which edges the fin above and below. ‘The 
inner rays are all deeply divided longitudinally and transversely 
articulated. The number of rays in the upper and lower lobe is 
equal, eight in both. ‘There seens however to be a middle ray, 
So that properly speaking there are seven rays in the upper lobe, 
one in the middle, and eight in the lower lobe. ’ 
The tail is deeply furcate. When the fin is shut, the inner- 
Most rays overlap each other, so that the caudal appears much 
Narrower than when fully expanded, but the outer rays in both 
obes remain in one plane, and do not overlap each other at all. 
The anal consists of two simple short rays in advance of the long 
the fins shnt until [ began to study the Balistidee, I am unable 
to say how far in varions families, the closing of the fius varies ; 
bat it isa point to which the attention of Zoologists should be 
directed in future, as it will no doubt afford interesting characters 
. Szcowp Senses, Vol. XIX, No. 55.—Jan., 1855. 
