NATURAL SCIENCES OF PHILADELPHIA. 83 



between which the membrane is acutely notched, the scaleless crown and 

 little development of the occipital crest, the dentition and the number of 

 branchiostegal rays, and, finally, the absence of axillar scales. With any 

 other form it is unnecessary to compare the genus, as its natural affinities 

 appear to be more intimate with Moronopsis* than any other. Naturalists can 

 decide from the above enumeration of the differential characters, in compari- 

 son with Moronopsis, if there is any other group to which it could be more 

 naturally approximated. If it is stated that the physiognomy of the two 

 genera is quite similar, the chief difference being caused by the procurrence 

 of the occipital crest and the rectilinear profile, as well as the character of 

 the scales, the ichthyologist can appreciate the aspect of the newly-described 

 form. 



Xenichthys xanti Gill. 



The greatest height equals three-tenths of the length (exclusive of the caudal). 

 The head forms a third of the same. The diameter of the eye equals a third 

 of the head's length, is about a third greater than the interorbital area, and 

 nearly a third greater than the length of the snout. The fourth or longest 

 dorsal spine equals nearly a fifth of the total length, and is nearly five times 

 longer than the tenth. The third or longest anal spine is scarcely more than 

 a twelfth of the length. The pectoral fin at least exceeds a seventh of the 

 length, while the ventral equals a seventh. 



D. XII. 14. A. III. 17. C. 11. I. 8. 7. I. 9. P. 1. 15. V. I. 5. 



Scales, lat. line 50. 



The color is light ; on each side of the back are two indistinct, purple, 

 longitudinal bands ; and before the dorsal fin is another. The color below is 

 silvery. At the base of the caudal there is an indistinct spot. The tip of the 

 spinous dorsal fin is dark. 



This most interesting and even remarkable type is dedicated to Mr. John 

 Xautus, to whom we are indebted for the noble collection of fishes and other 

 animals of Lower California, and who has, more than any other single man, 

 contributed to our knowledge of the natural history of the Western coast. 



Family CARANGOIDJE. 



Genus ARGYRIOSUS Lac. 



Two representatives of this genus are found on the Atlantic coast of the 

 United States : they are the A. vomer, of Linnasus, and the A. capillaris, Dekay, 

 the A. unimaculatus of Batchelder and Storer, and the form which has been 

 considered by Gunther as the young of A. vomer or a new species, appears to 

 me to be the young of Vomer selipinnis, and at least belongs to the same genus. 

 The Argyriosus Spixii of Castelnau is the unfortunate Selene argentea of Lace- 

 pede, first well made known by Mr. Brevoort, but which has received a num- 

 ber of names from different writers. 



Argyriosus Brevoortii Gill. 

 The greatest height in an oblique direction nearly equals nine-tenths ('87) 

 of the length in a straight line, from the vertical of the snout to the end of the 

 median caudal rays. The head forms less than a third of that length. The 

 profile is oblique, and slightly incurved below the angular crown ; its distance 

 from the vertical of the snout equals an eleventh of the total length, and be- 

 fore the eyes, two-thirds of the preceding. The diameter of the orbit equals 

 an eleventh of the length, and its distance from the profile equals two-thirds 

 of the diameter. The height of the preorbital is twice as great as the diame- 

 ter of the orbit. The base of the arched portion of the lateral line equals 

 three-tenths of the total length, and its elevation above the horizon equals a 



*The Datnia? ambigua of Kichanlson, which has been referred by Gunther to the genus Dules 

 differs from Moronopsis by the shorter convex anal fin, the large second anal spine, the small eyes 

 and the entire physiognomy. It may be called Plectropliles ambiguus. 



1863.] 



