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U. S. P. R. R. EXP. AND SURVEYS ZOOLOGY GENERAL REPORT. 



of a lighter, rather more yellowish tint. The caudal region is dark above and below. The fins 

 are likewise dark. 



List of specimens. 



SCOLECOSOMA, Girard. 



GEN. CHAR All the characters of Ammocoetes except the presence of one single dorsal fin instead of two, continuous with 

 the upper lobe of the caudal. The anal is likewise rudimentary, else reduced to a mere ridge extending from the vent to the 

 inferior lobe of the caudal. 



Three species, so far known, compose this genus: Ammocoetes concolor, KIRTL., from the 

 hydrographic basin of the Ohio river; Ammocoetes unicolor, DEKAY, from the fresh waters of 

 the northeastern States; and Ammocoetes borealis, AGASS., from Lake Superior. No repre 

 sentatives of it have, as yet, been observed west of the Mississippi valley. 



