FISHES—BLENNIDAE—XIPHIDION MUCOSUM. 
119 
parison with that of A. flavidus. The head is contained nearly ten times in the total length, 
thus seemingly smaller than in A. flaviclus, a feature also indicated by the lact that the mouth 
is smaller. The posterior extremity of the maxillar hone is said, by Dr. Ayres, to correspond 
to a vertical line which would intersect the pupil, whilst I find, upon the specimens now before 
me, that the said vertical line would have to be drawn rather more posteriorly. The origin of 
the dorsal is situated a little more forwards than in A. flavidus, the caudal fin being also some¬ 
what larger. The structure of the fins is, otherwise, identical in both species. 
There is no marked difference in the size of the scales, which are conspicuously pectinated, 
though so very small. 
As to the coloration, Dr. Ayres tells us that it is u almost uniform greenish olive, in some 
instances bright pea green. A narrow, vertical, black vitta runs from the lower border of the 
eye downwards; another, of similar breadth, from the upper border inwards and backwards to the 
occiput,” We observe, moreover, small blackish spots and dots irregularly dispersed over the 
sides of the body, and a double regular series of similar spots along the base and edge of the 
dorsal and anal fins. 
List of specimens. 
Catal. 
No. 
No. of 
specs. 
Sex and 
age. 
Locality. 
When 
collected. 
Whence obtained. 
Orig. 
No. 
Nature of 
specimens. 
Collected by— 
496 
2 
Adult.. 
San Francisco, Cal. 
1856 
Dr. W. 0. Ayres... 
22 
Alcoholic.... 
Dr. Ayres. 
XIPHIDION, Girard. 
Gen. Char. —Body very much elongated and very much compressed. Head small and sub-ovoid. Mouth large. Canine 
teeth in front of the jaws ; small and conical ones upon the branches of the premaxillaries (upper jaw) and dentaries (lower 
jaw), disposed upon a double row on the upper jaw and a single row on the lower jaw. Palatines and vomer toothless. Branchial 
apertures continuous under the throat. Dorsal fin spinous, and occupying nearly the whole length of the back, and contiguous 
to the caudal. Anal soft, without spinous rays anteriorly, and contiguous to the caudal also. Caudal small, exteriorly rounded. 
Ventral fins wanting. Pectorals very small. Scales, none ; several mucous lines. 
This genus resembles Gunnellus in its general appearance. The shape of the body and the 
structure of the dorsal fin are alike in every respect. The absence of spiny rays in advance of 
the anal is a feature peculiar, neither met with in Gunnellus nor in Apodichthys. It approxi¬ 
mates the latter, however, by the non-existence of the ventral fins. The pectorals themselves 
are a good deal smaller than in the genera just mentioned. As regards the dentition, it resem¬ 
bles more that of Apodichthys than lhat of Gunnellus, hut still differing from the former by the 
presence of canine upon the extremity of both jaws. The vomer and palatines, on the other hand, 
are toothless. The absence of scales, upon which we are left somewhat in doubt, would constitute 
another distinguishing feature. 
XIPHIDION MUCOSUM, Grd. 
Spec. Char. —Three lateral and one abdominal mucous ducts. Head sub-conical ; mouth large ; posterior extremity of 
maxillary extending to a vertical line drawn across the posterior rim of the orbit. Ground color olivaceous, clouded or macu¬ 
lated with blackish brown. Two post-ocular dark vittae crossing the cheek. 
The largest specimens before us measure seven inches in total length, and the smallest two 
inches, none of which being in a perfect state of preservation. Their number, however, has 
enabled us to form a correct idea of the general fascies of the present species. 
