420 EXPLORATIONS ACROSS THE GREAT BASIN OF UTAH. 



AMIURUS OBESUS, Gill. 



The boily is {■.on]])uralively short nnd robust. Tlie greatest height exceeds a fifth 

 of the total length from snout to margin of caudal. The least height of the caudal 

 peduncle equals a tenth of the length. The greatest thickness at the bases of the 

 pectoral fins exceeds a fiftli of the length. 



The head is almost semi-conical in profile, and is aljove oval and depressed, and 

 declines in nearly a straight line from the doi-sal fin to the snout. From the snout to 

 the bony margin of the operculum, it forms a quarter of the extreme length. The 

 greatest width exceeds a iifth of the total length; the width between the cheeks, under 

 the eyes, equals eighteen hundredths of the same. The interval between the borders 

 of the eyes exceeds thirteen hundredths. 



The eyes are small and covered with adipose matter; the diameter of one is equal 

 to about an eighth of the length of the head; they are separated from tlie middle of the 

 snout by more than a tenth of the total length. 



The maxillary barbels are slender and exteud little beyond tlie bases of the pec- 

 torals. The nasal l)arbels extend beyond the posterior borders of the eyes. The 

 infra-maxillary are arranged on a curved line parallel with the loAver jaw. The ex- 

 ternal are little longer than the internal, the former about equal the interval between 

 the eyes; the distance between the bases of the two internal exceeds by about a fourth 

 that between the internal and external of one side. 



The bran chiostegal rays are enveloped in a thiclc skin; tliere are nine, the two 

 upper of Avhich are large and compressed. The branchiostegal membrane is deeply 

 excavated, and, as in all the Icfaluri, when closed, or not expanded, appears anteriorly 

 as a simple fissure or fold; the mental fold if? much nearer the b(ittom of the emargination 

 than the jaw. The membrane itself is attaclied for nearly lialf the distance between 

 the fold and the emargination. 



The dorsal fin commences scarcely l)ehind the end of tlie first third of the length ; 

 its length nearly equals a twelfth of the length, as does also that of the spine; its height 

 is about a seventh of the length. 



The adipose fin is semi-cordiform. 



The anal fin commences at the fifty-four hundredths i)art of the distance between 

 the snout and end of caudal; its length equals a seventh of the total length, and its 

 height less than a thirteenth; it rapidly increases in height in front, and as rapidly 

 decreases behind. 



The pectoral fins are short, their length little exceeding a seventh of the total; the 

 spine equals an eleventh of the length, is moderately stout, externally edentulous, and 

 internally toothed. 



The process of tlie coracoid bone is spiniform, and from the l)ase of the pectoral 

 spine equals seven ninths of its length. 



The ventral fins commence slightly behind the fourth tentli of tlie length; they 

 equal a seventh of the length. The third ray is the longest. 



The caudal fin, when expanded, appears to be truncated, and forms fifteen hun- 

 dredths of the total length. 



D. I. 4}; A. 4. 13. i; C. 7. 1. 15. 1. 9; P. I. 8; V. 1. 7. 



