73 



October 1, 1860. 

 President in the Chair. 



Dr. Ayres presented the following paper : 



Atherinojjsis affinis (Ayres). — Two species o^ Atherinojjsis are 

 constantly sold in the markets of San Francisco, under the general 

 name of " Smelt." The specimens in the collection of the Smith- 

 sonian Institution, from which Girard drew his description of A. 

 calif orniensis, probably comprise both species, though the descrip- 

 tion is not sufficiently definite to settle the point. But inasmuch as 

 the figure which he gives represents without doubt the one which 

 does truly attain the length of " seventeen inches," it is better to 

 retain the name californiends for the largest of the two species, 

 Avhich is at the same time the more slender. The smaller species 

 may receive the name A. affinis ; the diagnostic characters are here 

 given side by side, for more ready comparison : 



Atheriuopsis affinis (Ayres). Fig. 18. 

 Greatest depth, not quite oue-fourth of 

 the total leno-th ; length of the head, 

 about one-tifth of the greatest depth. 



Gape of the mouth, extending back 

 but about half tlie distance from the snout 

 to the ej'e. (The size of the head rela- 

 tively to that of the body, and the actual 

 size of the mouth, are decidedly less in 

 affinis than in californiensis.) 



The tirst dorsal is nearlyits own length 

 further back, arising nearer to the tips of 

 the central caudal rays than to the snout. 



The height of the second dorsal is 

 equal to its length. 



The ventral rtns are larger, their height 

 being about one-tenth of the length of 

 the tisli. 



The pectoral fins are lai-ger, their 

 height being about two-elevenths of the 

 • total length. 



The flesh is iirmer, and the scales 

 larger and harder. 



Fig. 



Atherinopsis californiensis (Grd). 

 17. Greatest depth, a little more than 

 one-sixtli of the total length. Length of 

 the head, fully equal to the greatest depth. 



Gape of the mouth, extending back 

 about half the distance from the snout to 

 the middle of the j^iipil. 



Fii-st dorsal arising nearer to the snout 

 than to the tips of the central caudal 

 irays. 



The height of the second dorsal is a 

 little over two-thirds of its length. 



The height of the ventral tins is only 

 a little more than one-thirteenth of the 

 total length. 



The height of the pectoral fins is a lit- 

 tle more than two-thirteenths of the total 

 length. 



The principal points, therefore, by which A. affinis may be dis- 

 tinguished are, the stouter body, relatively smaller head and smaller 

 mouth, larger fins, larger scales, and firmer flesh. It is also a 

 smaller fish, never exceeding eight inches, so far as I have ob- 

 served, while A. californiensis is frequently fifteen inches long, and 

 occasionally seventeen. 



Both species are constantly in the markets in large numbers, and 

 in common with Osmerus jjretiosns (Grd.) and Osmerus thaleich- 

 tJii/s, (Ayres) ai'e sold indiscriminately as " smelt," though almost 

 all the fishermen are able to recognize the four species, and for 



