FISHES — BLENNIDAE — XIPHIDION MUCOSUM. 



119 



parison witli that of A, flavidus. The head is contained nearly ten times in the total length, 

 thus seemingly smaller than ia A. flavidus, a feature also indicated by the iact that the mouth 

 is smaller. The posterior extremity of the maxillar bone is said, by Dr. Ayrea, to correspond 

 to a vertical line which would intersect the pupil, whilst I iind, 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 difierence 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 "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. 



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 flower 

 jaw), disposed upon a double row on the upper jaw and a single row on the lower jaw. Palatines and vomer tootliless. 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 that of Gunnellus, but still difiering 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, G r d . 



Spec Char. — Three lateral and one abdominal raucous ducts. Head sub-conical ; mouth large ; posterior extremity of 

 maxillary extending to a vertical line drawn across the posterior rim of tlie 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. 



