MILNER FISHERIES OF THE GREAT LAKES. G9 



The variation iu the lateral series was withiu the numbers thirty and 

 thirty-nine, the most often-recurring number being thirty-four. In this 

 character it is well separated from A. oxyrhynchus, A. hrevirostris, A, 

 transmontanus, A. aciitirostHs. The number in the ventral series was 

 found to vary between eight and ten. From A. maculosus, of the Ohio 

 Eiver, a very constant character differing from A. rubicuiidus was ob- 

 served in the longer blades of the keels on the shields, the}" being pro- 

 longed backward and the points or hooks directed posteriorly-, while in 

 the lake species the keels are more central and their points rise nearly 

 vertically. 



In the obsolescence of the plates, certain species of the old world are 

 similar. Kirtland claims the same fact for the Ohio River sturgeon. 

 In a specimen of A. transmontanus, in the National Museum, the same 

 tendency is indicated, the plates of the body having becorae thin and 

 wafer-like and no appearance of the keels remaining, though in j'ounger 

 specimens the keels are prominent and shari)ly hooked. 



The skin throughout is covered with tooth-like points, and is unlike 

 other American species in the minuteness of these interserial ossiflca- 

 tious, except A. transmontanus and A. medirostris. 



The snout in the adults is very much obtuse and rounded, and its 

 cartilaginous extremity very little protected by plates. Its great reduc- 

 tion in length, with age, makes it an unreliable element iu calculating 

 the proportions of the body, and in the table of proportions it is, for this 

 reason, not included in the measurements of the specimen ; the propor- 

 tions of parts to the length of the trunk being calculated with refer- 

 ence to the distance from the opercular opening to the end of the lateral 

 series of plates, and the parts of the head to its length, are calculated 

 with reference to a measurement from the orbit to the posterior edge of 

 the opercular opening. 



(24 e.) Different characters in old and young sture/eons.— The great 

 number of species of sturgeons made by numerous authors has resulted 

 not alone from basing them on characters of insufficient value, but 

 from the great differences in the appearance of old and young 

 specimens. These differences are in the snout, which is, in young 

 specimens, long and slender, but whch, by being absorbed or tailing to 

 grow as rapidly as the rest of the body, in the large sturgeons has a 

 blunt and obtuse form; and in certain species, in the possession of large, 

 well-developed shields in the younger ones, and their gradual disap- 

 pearance as they mature and attain full size. 



Allusion has been made by Dr. Kirtland to the fact of the disappear- 

 ance of the shields in certain American species as the fish increased in 

 size. In accordance with this view, he placed the names of several species 

 of other naturalists as synonyms of A. rubicundus. This arrangement 

 was accepted by Storer and introduced iu his Synopsis of the Fishes of 

 North America. 



