Fishes of the Western North Atlantic 3 3 



western North Atlantic species. In American species, the development of the modified 

 predorsal shield increases in the following order: transmontanus (not only rudimentary, 

 but sometimes absent), brevh'ostris, fulvescens, oxyrhynchus, and medirostris. In the case 

 of the enlarged fulcrum along the lower lobe of the caudal and of the dermal ossifica- 

 tions, the order is brevirostris, fulvescens, transmontanus, oxyrhynchus, and medirostris. 



Explanation of Terms, Measurements, and Counts. In order to facilitate the use of 

 the Key and Descriptions, a brief explanation of certain terms and methods used in 

 measuring and counting follows. 



Regular rows of bony shields: The dorsal row and the lateral row on each side 

 are the most important from a taxonomic standpoint. The first shield in the dorsal row 

 corresponds to the occipital plate or nuchale, and the last is just in front of the modified 

 shield (see below) at the beginning of the dorsal fin. The first shield of the lateral 

 row, called the supracleithrum, borders the posterior margin of the branchial cavity; 

 although its size may vary, it is typically larger than the next posterior shield; its 

 spine is usually less developed than the spines on the shields posterior to it. The last 

 shield of the lateral row (a small one) is situated at the posterior extremity of the 

 caudal peduncle, just anterior to the shields that continue on from the lateral row 

 along the upper lobe of the caudal. 



The elongated fulcrum at the base of the lower caudal lobe (difficult to see on 

 large fish) is of considerable taxonomic importance when compared to the length of 

 the anal fin base. 



There are also modified shields at the beginning of both dorsal and anal fins; 

 these, because of their respective positions, can be called predorsal and preanal. The 

 one in front of the dorsal fin is more important from the taxonomic point of view; 

 this modified shield is oval in shape, has no median crest or spine, and its posterior end 

 is somewhat bent upwards to embrace the first dorsal ray; the anterior end is not forked 

 but does have a slight indentation. There are two or more preanal shields; the nearest 

 one to the fin is very similar in shape and structure to the predorsal shield; those farther 

 in front, according to the species, are present in pairs or in a single file; the disposition 

 of these preanal shields is the same as that for postdorsal shields (see below). 



Dermal ossifications: These small bony structures (ftn. 4), which vary in 

 size and shape with species and with age of fish, lie in the skin between the regular rows 

 of bony shields; they are best developed on the sides between the dorsal and lateral 

 rows. The degree of development, according to species, corresponds closely to that 

 of the regular bony shields. 



Total length (TL) is taken along the median line from the tip of the snout to 

 the posterior of the upper lobe of the tail when the fish is lying in a natural position. 

 Fork length (FL) is measured from the tip of the snout to the posterior end of the 

 median caudal rays — that is, to the fork of the tail. [In specimens less than five inches 

 (125 mm) FL, the lower caudal rays are still not fully developed and are therefore 

 short. The absence of the lower caudal lobe is not only typical of young oxyrhynchus 

 but of other Sturgeons as well. We observed this m fulvescens; and Grote, et al. (j6: 



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