384 



U. S. p. R. R. EXP. AND SDEVEYS — ZOOLOGY — GENERAL BEPOET. 



of a lighter, ratlier more yellowish tiat. The caudal regioQ is dark above and below. The fins 

 are likewise dark. 



List of specimens. 



SCOLECOSOMA, Girard. 



Gen. Char. All the characters of Jimmccoetes except the presence of one single dorsal fin instead of two, continuous with 



the upper lube 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 

 bydrographic basin of the Ohio river; Ammocoetes unicolor, DeK ay, irom the fresh waters of 

 the northeastern States; and Ammocoetes horealis, Agass., from Lake Superior. No repre- 

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



